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 $208.34   11.196%   $231.6657   $231.67   $231.65   $231.70  
  Purchase #2 $112.98   8.563%   $122.6545   $122.65   $122.65   $122.70  
  Purchase #3 $121.46   3.343%   $125.5204   $125.52   $125.50   $125.50  
  Purchase #4 $70.75   3.315%   $73.0954   $73.10   $73.10   $73.10  
  Purchase #5 $108.83   9.486%   $119.1536   $119.15   $119.15   $119.20  
  Purchase #6 $168.52   6.587%   $179.6204   $179.62   $179.60   $179.60  
  Purchase #7 $93.74   4.138%   $97.619   $97.62   $97.60   $97.60  
  7 purchase totals = $884.62       $949.3290   $949.33   $949.25   $949.40