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 $112.46   12.377%   $126.3792   $126.38   $126.40   $126.40  
  Purchase #2 $99.26   6.798%   $106.0077   $106.01   $106.00   $106.00  
  Purchase #3 $154.47   4.827%   $161.9263   $161.93   $161.95   $161.90  
  Purchase #4 $235.89   11.742%   $263.5882   $263.59   $263.60   $263.60  
  Purchase #5 $66.73   9.689%   $73.1955   $73.20   $73.20   $73.20  
  Purchase #6 $144.75   7.786%   $156.0202   $156.02   $156.00   $156.00  
  Purchase #7 $68.45   11.840%   $76.5545   $76.55   $76.55   $76.60  
  7 purchase totals = $882.01       $963.6716   $963.68   $963.70   $963.70