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 $241.41   11.701%   $269.6574   $269.66   $269.65   $269.70  
  Purchase #2 $208.60   4.854%   $218.7254   $218.73   $218.75   $218.70  
  Purchase #3 $146.39   10.644%   $161.9718   $161.97   $161.95   $162.00  
  Purchase #4 $43.69   9.488%   $47.8353   $47.84   $47.85   $47.80  
  Purchase #5 $185.29   13.569%   $210.432   $210.43   $210.45   $210.40  
  Purchase #6 $54.66   7.831%   $58.9404   $58.94   $58.95   $58.90  
  Purchase #7 $12.55   4.265%   $13.0853   $13.09   $13.10   $13.10  
  7 purchase totals = $892.59       $980.6476   $980.66   $980.70   $980.60