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 $249.60   4.547%   $260.9493   $260.95   $260.95   $260.90  
  Purchase #2 $51.67   7.518%   $55.5546   $55.55   $55.55   $55.60  
  Purchase #3 $111.43   12.709%   $125.5916   $125.59   $125.60   $125.60  
  Purchase #4 $207.98   4.227%   $216.7713   $216.77   $216.75   $216.80  
  Purchase #5 $199.76   13.311%   $226.3501   $226.35   $226.35   $226.40  
  Purchase #6 $184.67   12.842%   $208.3853   $208.39   $208.40   $208.40  
  Purchase #7 $161.41   5.246%   $169.8776   $169.88   $169.90   $169.90  
  7 purchase totals = $1,166.52       $1,263.4798   $1,263.48   $1,263.50   $1,263.60