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 $46.39   8.309%   $50.2445   $50.24   $50.25   $50.20  
  Purchase #2 $188.30   12.148%   $211.1747   $211.17   $211.15   $211.20  
  Purchase #3 $123.42   12.358%   $138.6722   $138.67   $138.65   $138.70  
  Purchase #4 $190.69   8.667%   $207.2171   $207.22   $207.20   $207.20  
  Purchase #5 $229.29   3.203%   $236.6342   $236.63   $236.65   $236.60  
  Purchase #6 $247.34   8.563%   $268.5197   $268.52   $268.50   $268.50  
  Purchase #7 $132.31   6.618%   $141.0663   $141.07   $141.05   $141.10  
  7 purchase totals = $1,157.74       $1,253.5287   $1,253.52   $1,253.45   $1,253.50