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 $124.91   12.505%   $140.53   $140.53   $140.55   $140.50  
  Purchase #2 $88.69   5.522%   $93.5875   $93.59   $93.60   $93.60  
  Purchase #3 $81.30   8.244%   $88.0024   $88.00   $88.00   $88.00  
  Purchase #4 $76.44   6.342%   $81.2878   $81.29   $81.30   $81.30  
  Purchase #5 $132.90   13.778%   $151.211   $151.21   $151.20   $151.20  
  Purchase #6 $197.89   4.833%   $207.454   $207.45   $207.45   $207.50  
  Purchase #7 $38.29   3.793%   $39.7423   $39.74   $39.75   $39.70  
  7 purchase totals = $740.42       $801.8150   $801.81   $801.85   $801.80