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 $122.68   4.700%   $128.446   $128.45   $128.45   $128.40  
  Purchase #2 $243.66   10.178%   $268.4597   $268.46   $268.45   $268.50  
  Purchase #3 $97.58   13.551%   $110.8031   $110.80   $110.80   $110.80  
  Purchase #4 $34.91   5.194%   $36.7232   $36.72   $36.70   $36.70  
  Purchase #5 $235.33   11.756%   $262.9954   $263.00   $263.00   $263.00  
  Purchase #6 $18.90   11.871%   $21.1436   $21.14   $21.15   $21.10  
  Purchase #7 $32.97   11.149%   $36.6458   $36.65   $36.65   $36.60  
  7 purchase totals = $786.03       $865.2168   $865.22   $865.20   $865.10