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 $46.87   8.532%   $50.8689   $50.87   $50.85   $50.90  
  Purchase #2 $250.70   7.441%   $269.3546   $269.35   $269.35   $269.40  
  Purchase #3 $144.45   11.111%   $160.4998   $160.50   $160.50   $160.50  
  Purchase #4 $54.34   8.519%   $58.9692   $58.97   $58.95   $59.00  
  Purchase #5 $150.80   4.705%   $157.8951   $157.90   $157.90   $157.90  
  Purchase #6 $57.71   10.752%   $63.915   $63.92   $63.90   $63.90  
  Purchase #7 $27.86   10.784%   $30.8644   $30.86   $30.85   $30.90  
  7 purchase totals = $732.73       $792.3670   $792.37   $792.30   $792.50