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 $55.99   4.666%   $58.6025   $58.60   $58.60   $58.60  
  Purchase #2 $76.81   10.129%   $84.5901   $84.59   $84.60   $84.60  
  Purchase #3 $98.26   13.216%   $111.246   $111.25   $111.25   $111.20  
  Purchase #4 $195.30   10.564%   $215.9315   $215.93   $215.95   $215.90  
  Purchase #5 $170.91   11.854%   $191.1697   $191.17   $191.15   $191.20  
  Purchase #6 $97.94   13.489%   $111.1511   $111.15   $111.15   $111.20  
  Purchase #7 $18.97   3.458%   $19.626   $19.63   $19.65   $19.60  
  7 purchase totals = $714.18       $792.3169   $792.32   $792.35   $792.30