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 $88.54   4.203%   $92.2613   $92.26   $92.25   $92.30  
  Purchase #2 $156.61   6.228%   $166.3637   $166.36   $166.35   $166.40  
  Purchase #3 $233.62   5.142%   $245.6327   $245.63   $245.65   $245.60  
  Purchase #4 $16.36   5.273%   $17.2227   $17.22   $17.20   $17.20  
  Purchase #5 $192.64   8.484%   $208.9836   $208.98   $209.00   $209.00  
  Purchase #6 $144.71   3.402%   $149.633   $149.63   $149.65   $149.60  
  Purchase #7 $15.34   11.376%   $17.0851   $17.09   $17.10   $17.10  
  7 purchase totals = $847.82       $897.1821   $897.17   $897.20   $897.20