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 $124.82   8.773%   $135.7705   $135.77   $135.75   $135.80  
  Purchase #2 $164.40   10.864%   $182.2604   $182.26   $182.25   $182.30  
  Purchase #3 $14.78   5.832%   $15.642   $15.64   $15.65   $15.60  
  Purchase #4 $125.62   10.834%   $139.2297   $139.23   $139.25   $139.20  
  Purchase #5 $30.73   3.316%   $31.749   $31.75   $31.75   $31.70  
  Purchase #6 $201.84   6.282%   $214.5196   $214.52   $214.50   $214.50  
  Purchase #7 $185.70   11.348%   $206.7732   $206.77   $206.75   $206.80  
  7 purchase totals = $847.89       $925.9444   $925.94   $925.90   $925.90