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 $150.52   7.187%   $161.3379   $161.34   $161.35   $161.30  
  Purchase #2 $174.63   12.268%   $196.0536   $196.05   $196.05   $196.10  
  Purchase #3 $249.41   5.204%   $262.3893   $262.39   $262.40   $262.40  
  Purchase #4 $144.97   3.162%   $149.554   $149.55   $149.55   $149.60  
  Purchase #5 $58.52   4.675%   $61.2558   $61.26   $61.25   $61.30  
  Purchase #6 $236.70   4.610%   $247.6119   $247.61   $247.60   $247.60  
  Purchase #7 $122.52   11.507%   $136.6184   $136.62   $136.60   $136.60  
  7 purchase totals = $1,137.27       $1,214.8209   $1,214.82   $1,214.80   $1,214.90