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 $51.95   12.660%   $58.5269   $58.53   $58.55   $58.50  
  Purchase #2 $180.65   12.526%   $203.2782   $203.28   $203.30   $203.30  
  Purchase #3 $106.37   7.460%   $114.3052   $114.31   $114.30   $114.30  
  Purchase #4 $89.63   6.613%   $95.5572   $95.56   $95.55   $95.60  
  Purchase #5 $135.34   11.171%   $150.4588   $150.46   $150.45   $150.50  
  Purchase #6 $52.96   10.332%   $58.4318   $58.43   $58.45   $58.40  
  Purchase #7 $184.26   11.238%   $204.9671   $204.97   $204.95   $205.00  
  7 purchase totals = $801.16       $885.5252   $885.54   $885.55   $885.60