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 $150.64   5.425%   $158.8122   $158.81   $158.80   $158.80  
  Purchase #2 $162.99   8.436%   $176.7398   $176.74   $176.75   $176.70  
  Purchase #3 $131.84   3.403%   $136.3265   $136.33   $136.35   $136.30  
  Purchase #4 $83.76   7.604%   $90.1291   $90.13   $90.15   $90.10  
  Purchase #5 $139.38   12.238%   $156.4373   $156.44   $156.45   $156.40  
  Purchase #6 $100.29   9.825%   $110.1435   $110.14   $110.15   $110.10  
  Purchase #7 $125.91   12.706%   $141.9081   $141.91   $141.90   $141.90  
  7 purchase totals = $894.81       $970.4965   $970.50   $970.55   $970.30