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 $33.35   4.507%   $34.8531   $34.85   $34.85   $34.90  
  Purchase #2 $201.48   8.302%   $218.2069   $218.21   $218.20   $218.20  
  Purchase #3 $67.30   10.300%   $74.2319   $74.23   $74.25   $74.20  
  Purchase #4 $118.38   5.267%   $124.6151   $124.62   $124.60   $124.60  
  Purchase #5 $79.73   3.176%   $82.2622   $82.26   $82.25   $82.30  
  Purchase #6 $188.99   5.279%   $198.9668   $198.97   $198.95   $199.00  
  Purchase #7 $194.81   13.490%   $221.0899   $221.09   $221.10   $221.10  
  7 purchase totals = $884.04       $954.2259   $954.23   $954.20   $954.30