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 $151.42   9.418%   $165.6807   $165.68   $165.70   $165.70  
  Purchase #2 $233.53   4.288%   $243.5438   $243.54   $243.55   $243.50  
  Purchase #3 $162.28   7.435%   $174.3455   $174.35   $174.35   $174.30  
  Purchase #4 $28.60   8.493%   $31.029   $31.03   $31.05   $31.00  
  Purchase #5 $43.71   9.291%   $47.7711   $47.77   $47.75   $47.80  
  Purchase #6 $9.70   4.573%   $10.1436   $10.14   $10.15   $10.10  
  Purchase #7 $237.95   10.254%   $262.3494   $262.35   $262.35   $262.30  
  7 purchase totals = $867.19       $934.8631   $934.86   $934.90   $934.70