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 $114.45   10.308%   $126.2475   $126.25   $126.25   $126.20  
  Purchase #2 $76.78   13.104%   $86.8413   $86.84   $86.85   $86.80  
  Purchase #3 $25.38   7.816%   $27.3637   $27.36   $27.35   $27.40  
  Purchase #4 $16.27   13.269%   $18.4289   $18.43   $18.45   $18.40  
  Purchase #5 $60.60   4.219%   $63.1567   $63.16   $63.15   $63.20  
  Purchase #6 $141.40   3.468%   $146.3038   $146.30   $146.30   $146.30  
  Purchase #7 $185.88   7.711%   $200.2132   $200.21   $200.20   $200.20  
  7 purchase totals = $620.76       $668.5551   $668.55   $668.55   $668.50