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 $55.79   13.353%   $63.2396   $63.24   $63.25   $63.20  
  Purchase #2 $189.56   4.207%   $197.5348   $197.53   $197.55   $197.50  
  Purchase #3 $102.72   10.350%   $113.3515   $113.35   $113.35   $113.40  
  Purchase #4 $165.56   12.173%   $185.7136   $185.71   $185.70   $185.70  
  Purchase #5 $60.59   4.754%   $63.4704   $63.47   $63.45   $63.50  
  Purchase #6 $156.65   10.595%   $173.2471   $173.25   $173.25   $173.20  
  Purchase #7 $94.83   7.419%   $101.8654   $101.87   $101.85   $101.90  
  7 purchase totals = $825.70       $898.4224   $898.42   $898.40   $898.40