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 $85.61   7.782%   $92.2722   $92.27   $92.25   $92.30  
  Purchase #2 $196.41   8.198%   $212.5117   $212.51   $212.50   $212.50  
  Purchase #3 $119.66   13.775%   $136.1432   $136.14   $136.15   $136.10  
  Purchase #4 $199.57   7.373%   $214.2843   $214.28   $214.30   $214.30  
  Purchase #5 $149.68   13.864%   $170.4316   $170.43   $170.45   $170.40  
  Purchase #6 $206.84   13.741%   $235.2619   $235.26   $235.25   $235.30  
  Purchase #7 $154.27   4.824%   $161.712   $161.71   $161.70   $161.70  
  7 purchase totals = $1,112.04       $1,222.6169   $1,222.60   $1,222.60   $1,222.60