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 $112.80   11.869%   $126.1882   $126.19   $126.20   $126.20  
  Purchase #2 $48.57   10.456%   $53.6485   $53.65   $53.65   $53.60  
  Purchase #3 $211.32   8.778%   $229.8697   $229.87   $229.85   $229.90  
  Purchase #4 $130.61   8.203%   $141.3239   $141.32   $141.30   $141.30  
  Purchase #5 $12.68   10.388%   $13.9972   $14.00   $14.00   $14.00  
  Purchase #6 $78.64   3.556%   $81.4364   $81.44   $81.45   $81.40  
  Purchase #7 $80.68   11.743%   $90.1543   $90.15   $90.15   $90.20  
  7 purchase totals = $675.30       $736.6182   $736.62   $736.60   $736.60