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 $82.77   13.631%   $94.0524   $94.05   $94.05   $94.10  
  Purchase #2 $63.91   5.192%   $67.2282   $67.23   $67.25   $67.20  
  Purchase #3 $59.28   9.145%   $64.7012   $64.70   $64.70   $64.70  
  Purchase #4 $94.27   8.265%   $102.0614   $102.06   $102.05   $102.10  
  Purchase #5 $32.75   3.644%   $33.9434   $33.94   $33.95   $33.90  
  Purchase #6 $38.68   5.758%   $40.9072   $40.91   $40.90   $40.90  
  Purchase #7 $179.55   8.222%   $194.3126   $194.31   $194.30   $194.30  
  7 purchase totals = $551.21       $597.2064   $597.20   $597.20   $597.20