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 $58.97   7.746%   $63.5378   $63.54   $63.55   $63.50  
  Purchase #2 $213.97   3.645%   $221.7692   $221.77   $221.75   $221.80  
  Purchase #3 $154.69   8.227%   $167.4163   $167.42   $167.40   $167.40  
  Purchase #4 $204.41   3.634%   $211.8383   $211.84   $211.85   $211.80  
  Purchase #5 $169.36   7.706%   $182.4109   $182.41   $182.40   $182.40  
  Purchase #6 $44.60   10.581%   $49.3191   $49.32   $49.30   $49.30  
  Purchase #7 $94.97   3.344%   $98.1458   $98.15   $98.15   $98.10  
  7 purchase totals = $940.97       $994.4374   $994.45   $994.40   $994.30