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 $227.82   11.463%   $253.935   $253.94   $253.95   $253.90  
  Purchase #2 $40.98   11.619%   $45.7415   $45.74   $45.75   $45.70  
  Purchase #3 $164.69   7.348%   $176.7914   $176.79   $176.80   $176.80  
  Purchase #4 $79.75   10.787%   $88.3526   $88.35   $88.35   $88.40  
  Purchase #5 $22.72   9.440%   $24.8648   $24.86   $24.85   $24.90  
  Purchase #6 $53.97   8.507%   $58.5612   $58.56   $58.55   $58.60  
  Purchase #7 $150.34   5.109%   $158.0209   $158.02   $158.00   $158.00  
  7 purchase totals = $740.27       $806.2674   $806.26   $806.25   $806.30