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 $171.25   13.754%   $194.8037   $194.80   $194.80   $194.80  
  Purchase #2 $76.49   6.241%   $81.2637   $81.26   $81.25   $81.30  
  Purchase #3 $180.93   7.496%   $194.4925   $194.49   $194.50   $194.50  
  Purchase #4 $187.70   13.634%   $213.291   $213.29   $213.30   $213.30  
  Purchase #5 $6.49   4.830%   $6.8035   $6.80   $6.80   $6.80  
  Purchase #6 $31.32   4.404%   $32.6993   $32.70   $32.70   $32.70  
  Purchase #7 $179.64   3.464%   $185.8627   $185.86   $185.85   $185.90  
  7 purchase totals = $833.82       $909.2164   $909.20   $909.20   $909.30