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 $29.82   9.416%   $32.6279   $32.63   $32.65   $32.60  
  Purchase #2 $149.82   5.709%   $158.3732   $158.37   $158.35   $158.40  
  Purchase #3 $91.73   10.693%   $101.5387   $101.54   $101.55   $101.50  
  Purchase #4 $115.75   4.325%   $120.7562   $120.76   $120.75   $120.80  
  Purchase #5 $51.58   7.794%   $55.6001   $55.60   $55.60   $55.60  
  Purchase #6 $159.62   11.392%   $177.8039   $177.80   $177.80   $177.80  
  Purchase #7 $162.91   9.753%   $178.7986   $178.80   $178.80   $178.80  
  7 purchase totals = $761.23       $825.4986   $825.50   $825.50   $825.50