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 $125.94   12.643%   $141.8626   $141.86   $141.85   $141.90  
  Purchase #2 $170.65   13.244%   $193.2509   $193.25   $193.25   $193.30  
  Purchase #3 $8.66   12.253%   $9.7211   $9.72   $9.70   $9.70  
  Purchase #4 $120.99   9.571%   $132.57   $132.57   $132.55   $132.60  
  Purchase #5 $10.62   13.863%   $12.0923   $12.09   $12.10   $12.10  
  Purchase #6 $183.35   13.645%   $208.3681   $208.37   $208.35   $208.40  
  Purchase #7 $92.56   4.231%   $96.4762   $96.48   $96.50   $96.50  
  7 purchase totals = $712.77       $794.3412   $794.34   $794.30   $794.50