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 $229.77   6.541%   $244.7993   $244.80   $244.80   $244.80  
  Purchase #2 $53.35   11.732%   $59.609   $59.61   $59.60   $59.60  
  Purchase #3 $36.94   10.564%   $40.8423   $40.84   $40.85   $40.80  
  Purchase #4 $190.67   6.260%   $202.6059   $202.61   $202.60   $202.60  
  Purchase #5 $19.80   4.847%   $20.7597   $20.76   $20.75   $20.80  
  Purchase #6 $9.68   11.284%   $10.7723   $10.77   $10.75   $10.80  
  Purchase #7 $213.44   10.610%   $236.086   $236.09   $236.10   $236.10  
  7 purchase totals = $753.65       $815.4745   $815.48   $815.45   $815.50