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 $39.47   12.815%   $44.5281   $44.53   $44.55   $44.50  
  Purchase #2 $22.76   4.754%   $23.842   $23.84   $23.85   $23.80  
  Purchase #3 $33.97   4.247%   $35.4127   $35.41   $35.40   $35.40  
  Purchase #4 $244.62   9.522%   $267.9127   $267.91   $267.90   $267.90  
  Purchase #5 $77.90   13.279%   $88.2443   $88.24   $88.25   $88.20  
  Purchase #6 $242.29   5.779%   $256.2919   $256.29   $256.30   $256.30  
  Purchase #7 $159.33   7.293%   $170.9499   $170.95   $170.95   $170.90  
  7 purchase totals = $820.34       $887.1816   $887.17   $887.20   $887.00