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 $92.35   6.308%   $98.1754   $98.18   $98.20   $98.20  
  Purchase #2 $115.62   8.345%   $125.2685   $125.27   $125.25   $125.30  
  Purchase #3 $185.56   4.163%   $193.2849   $193.28   $193.30   $193.30  
  Purchase #4 $115.76   7.660%   $124.6272   $124.63   $124.65   $124.60  
  Purchase #5 $116.44   10.650%   $128.8409   $128.84   $128.85   $128.80  
  Purchase #6 $39.82   9.464%   $43.5886   $43.59   $43.60   $43.60  
  Purchase #7 $34.80   7.479%   $37.4027   $37.40   $37.40   $37.40  
  7 purchase totals = $700.35       $751.1882   $751.19   $751.25   $751.20