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 $53.82   6.844%   $57.5034   $57.50   $57.50   $57.50  
  Purchase #2 $178.73   4.497%   $186.7675   $186.77   $186.75   $186.80  
  Purchase #3 $110.94   3.566%   $114.8961   $114.90   $114.90   $114.90  
  Purchase #4 $98.49   4.313%   $102.7379   $102.74   $102.75   $102.70  
  Purchase #5 $207.98   4.799%   $217.961   $217.96   $217.95   $218.00  
  Purchase #6 $118.68   4.641%   $124.1879   $124.19   $124.20   $124.20  
  Purchase #7 $222.61   6.218%   $236.4519   $236.45   $236.45   $236.50  
  7 purchase totals = $991.25       $1,040.5057   $1,040.51   $1,040.50   $1,040.60