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 $68.25   13.115%   $77.201   $77.20   $77.20   $77.20  
  Purchase #2 $6.95   7.848%   $7.4954   $7.50   $7.50   $7.50  
  Purchase #3 $77.78   8.497%   $84.389   $84.39   $84.40   $84.40  
  Purchase #4 $119.58   13.207%   $135.3729   $135.37   $135.35   $135.40  
  Purchase #5 $67.42   10.513%   $74.5079   $74.51   $74.50   $74.50  
  Purchase #6 $232.89   3.741%   $241.6024   $241.60   $241.60   $241.60  
  Purchase #7 $110.60   4.384%   $115.4487   $115.45   $115.45   $115.40  
  7 purchase totals = $683.47       $736.0173   $736.02   $736.00   $736.00