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 $172.37   12.539%   $193.9835   $193.98   $194.00   $194.00  
  Purchase #2 $101.65   11.498%   $113.3377   $113.34   $113.35   $113.30  
  Purchase #3 $103.97   4.156%   $108.291   $108.29   $108.30   $108.30  
  Purchase #4 $162.98   10.135%   $179.498   $179.50   $179.50   $179.50  
  Purchase #5 $61.39   8.215%   $66.4332   $66.43   $66.45   $66.40  
  Purchase #6 $59.39   10.551%   $65.6562   $65.66   $65.65   $65.70  
  Purchase #7 $102.37   11.857%   $114.508   $114.51   $114.50   $114.50  
  7 purchase totals = $764.12       $841.7076   $841.71   $841.75   $841.70