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 $92.41   4.421%   $96.4954   $96.50   $96.50   $96.50  
  Purchase #2 $63.72   12.778%   $71.8621   $71.86   $71.85   $71.90  
  Purchase #3 $35.84   5.433%   $37.7872   $37.79   $37.80   $37.80  
  Purchase #4 $193.77   12.497%   $217.9854   $217.99   $218.00   $218.00  
  Purchase #5 $94.73   4.231%   $98.738   $98.74   $98.75   $98.70  
  Purchase #6 $225.76   12.285%   $253.4946   $253.49   $253.50   $253.50  
  Purchase #7 $230.67   4.842%   $241.839   $241.84   $241.85   $241.80  
  7 purchase totals = $936.90       $1,018.2017   $1,018.21   $1,018.25   $1,018.20