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 $232.26   12.246%   $260.7026   $260.70   $260.70   $260.70  
  Purchase #2 $131.97   12.447%   $148.3963   $148.40   $148.40   $148.40  
  Purchase #3 $49.87   9.807%   $54.7608   $54.76   $54.75   $54.80  
  Purchase #4 $109.82   5.551%   $115.9161   $115.92   $115.90   $115.90  
  Purchase #5 $216.72   11.457%   $241.5496   $241.55   $241.55   $241.50  
  Purchase #6 $200.92   5.317%   $211.6029   $211.60   $211.60   $211.60  
  Purchase #7 $217.85   9.195%   $237.8813   $237.88   $237.90   $237.90  
  7 purchase totals = $1,159.41       $1,270.8096   $1,270.81   $1,270.80   $1,270.80