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 $189.32   9.549%   $207.3982   $207.40   $207.40   $207.40  
  Purchase #2 $241.78   3.697%   $250.7186   $250.72   $250.70   $250.70  
  Purchase #3 $78.65   4.307%   $82.0375   $82.04   $82.05   $82.00  
  Purchase #4 $197.71   13.580%   $224.559   $224.56   $224.55   $224.60  
  Purchase #5 $165.45   3.419%   $171.1067   $171.11   $171.10   $171.10  
  Purchase #6 $184.69   10.313%   $203.7371   $203.74   $203.75   $203.70  
  Purchase #7 $108.25   7.852%   $116.7498   $116.75   $116.75   $116.70  
  7 purchase totals = $1,165.85       $1,256.3069   $1,256.32   $1,256.30   $1,256.20