Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $152.64   13.707%   $173.5624   $173.56   $173.55   $173.60  
  Purchase #2 $248.57   5.669%   $262.6614   $262.66   $262.65   $262.70  
  Purchase #3 $190.31   4.627%   $199.1156   $199.12   $199.10   $199.10  
  Purchase #4 $219.83   4.551%   $229.8345   $229.83   $229.85   $229.80  
  Purchase #5 $219.30   13.434%   $248.7608   $248.76   $248.75   $248.80  
  Purchase #6 $168.91   13.846%   $192.2973   $192.30   $192.30   $192.30  
  Purchase #7 $110.69   8.849%   $120.485   $120.49   $120.50   $120.50  
  7 purchase totals = $1,310.25       $1,426.7170   $1,426.72   $1,426.70   $1,426.80