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 $214.68   13.797%   $244.2994   $244.30   $244.30   $244.30  
  Purchase #2 $229.85   4.846%   $240.9885   $240.99   $241.00   $241.00  
  Purchase #3 $147.99   7.816%   $159.5569   $159.56   $159.55   $159.60  
  Purchase #4 $170.68   7.621%   $183.6875   $183.69   $183.70   $183.70  
  Purchase #5 $221.60   13.494%   $251.5027   $251.50   $251.50   $251.50  
  Purchase #6 $93.55   7.285%   $100.3651   $100.37   $100.35   $100.40  
  Purchase #7 $75.64   3.336%   $78.1634   $78.16   $78.15   $78.20  
  7 purchase totals = $1,153.99       $1,258.5635   $1,258.57   $1,258.55   $1,258.70