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 $246.95   3.569%   $255.7636   $255.76   $255.75   $255.80  
  Purchase #2 $112.66   11.207%   $125.2858   $125.29   $125.30   $125.30  
  Purchase #3 $221.64   9.693%   $243.1236   $243.12   $243.10   $243.10  
  Purchase #4 $189.25   8.453%   $205.2473   $205.25   $205.25   $205.20  
  Purchase #5 $53.99   13.455%   $61.2544   $61.25   $61.25   $61.30  
  Purchase #6 $45.82   10.290%   $50.5349   $50.53   $50.55   $50.50  
  Purchase #7 $164.51   11.565%   $183.5356   $183.54   $183.55   $183.50  
  7 purchase totals = $1,034.82       $1,124.7452   $1,124.74   $1,124.75   $1,124.70