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 $194.30   11.779%   $217.1866   $217.19   $217.20   $217.20  
  Purchase #2 $101.47   13.390%   $115.0568   $115.06   $115.05   $115.10  
  Purchase #3 $87.50   12.549%   $98.4804   $98.48   $98.50   $98.50  
  Purchase #4 $123.27   3.709%   $127.8421   $127.84   $127.85   $127.80  
  Purchase #5 $156.27   3.443%   $161.6504   $161.65   $161.65   $161.70  
  Purchase #6 $217.93   11.229%   $242.4014   $242.40   $242.40   $242.40  
  Purchase #7 $108.78   3.569%   $112.6624   $112.66   $112.65   $112.70  
  7 purchase totals = $989.52       $1,075.2801   $1,075.28   $1,075.30   $1,075.40