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 $242.30   10.508%   $267.7609   $267.76   $267.75   $267.80  
  Purchase #2 $68.73   6.392%   $73.1232   $73.12   $73.10   $73.10  
  Purchase #3 $24.66   6.279%   $26.2084   $26.21   $26.20   $26.20  
  Purchase #4 $90.30   3.370%   $93.3431   $93.34   $93.35   $93.30  
  Purchase #5 $109.28   3.608%   $113.2228   $113.22   $113.20   $113.20  
  Purchase #6 $187.54   6.315%   $199.3832   $199.38   $199.40   $199.40  
  Purchase #7 $170.25   7.263%   $182.6153   $182.62   $182.60   $182.60  
  7 purchase totals = $893.06       $955.6569   $955.65   $955.60   $955.60