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 $53.63   13.610%   $60.929   $60.93   $60.95   $60.90  
  Purchase #2 $13.30   7.419%   $14.2867   $14.29   $14.30   $14.30  
  Purchase #3 $148.36   11.836%   $165.9199   $165.92   $165.90   $165.90  
  Purchase #4 $239.85   12.650%   $270.191   $270.19   $270.20   $270.20  
  Purchase #5 $238.63   11.429%   $265.903   $265.90   $265.90   $265.90  
  Purchase #6 $122.76   5.306%   $129.2736   $129.27   $129.25   $129.30  
  Purchase #7 $72.41   7.198%   $77.6221   $77.62   $77.60   $77.60  
  7 purchase totals = $888.94       $984.1253   $984.12   $984.10   $984.10