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 $28.88   12.833%   $32.5862   $32.59   $32.60   $32.60  
  Purchase #2 $57.53   9.543%   $63.0201   $63.02   $63.00   $63.00  
  Purchase #3 $83.89   12.181%   $94.1086   $94.11   $94.10   $94.10  
  Purchase #4 $114.68   9.847%   $125.9725   $125.97   $125.95   $126.00  
  Purchase #5 $52.58   13.332%   $59.59   $59.59   $59.60   $59.60  
  Purchase #6 $150.92   9.482%   $165.2302   $165.23   $165.25   $165.20  
  Purchase #7 $140.66   11.545%   $156.8992   $156.90   $156.90   $156.90  
  7 purchase totals = $629.14       $697.4068   $697.41   $697.40   $697.40