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 $227.26   11.689%   $253.8244   $253.82   $253.80   $253.80  
  Purchase #2 $60.78   6.682%   $64.8413   $64.84   $64.85   $64.80  
  Purchase #3 $50.94   12.671%   $57.3946   $57.39   $57.40   $57.40  
  Purchase #4 $59.68   13.496%   $67.7344   $67.73   $67.75   $67.70  
  Purchase #5 $213.93   5.244%   $225.1485   $225.15   $225.15   $225.10  
  Purchase #6 $125.94   6.200%   $133.7483   $133.75   $133.75   $133.70  
  Purchase #7 $110.79   3.475%   $114.64   $114.64   $114.65   $114.60  
  7 purchase totals = $849.32       $917.3315   $917.32   $917.35   $917.10