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 $217.52   11.842%   $243.2787   $243.28   $243.30   $243.30  
  Purchase #2 $74.38   8.396%   $80.6249   $80.62   $80.60   $80.60  
  Purchase #3 $162.37   10.348%   $179.172   $179.17   $179.15   $179.20  
  Purchase #4 $32.55   10.485%   $35.9629   $35.96   $35.95   $36.00  
  Purchase #5 $109.94   11.873%   $122.9932   $122.99   $123.00   $123.00  
  Purchase #6 $9.59   6.797%   $10.2418   $10.24   $10.25   $10.20  
  Purchase #7 $55.47   12.481%   $62.3932   $62.39   $62.40   $62.40  
  7 purchase totals = $661.82       $734.6667   $734.65   $734.65   $734.70