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 $86.48   12.845%   $97.5884   $97.59   $97.60   $97.60  
  Purchase #2 $113.33   11.821%   $126.7267   $126.73   $126.75   $126.70  
  Purchase #3 $51.98   13.613%   $59.056   $59.06   $59.05   $59.10  
  Purchase #4 $68.27   6.485%   $72.6973   $72.70   $72.70   $72.70  
  Purchase #5 $106.98   11.372%   $119.1458   $119.15   $119.15   $119.10  
  Purchase #6 $179.65   8.688%   $195.258   $195.26   $195.25   $195.30  
  Purchase #7 $170.75   12.257%   $191.6788   $191.68   $191.70   $191.70  
  7 purchase totals = $777.44       $862.1510   $862.17   $862.20   $862.20