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 $91.70   3.410%   $94.827   $94.83   $94.85   $94.80  
  Purchase #2 $186.48   13.294%   $211.2707   $211.27   $211.25   $211.30  
  Purchase #3 $82.67   4.605%   $86.477   $86.48   $86.50   $86.50  
  Purchase #4 $196.46   13.478%   $222.9389   $222.94   $222.95   $222.90  
  Purchase #5 $215.99   10.199%   $238.0188   $238.02   $238.00   $238.00  
  Purchase #6 $77.86   8.117%   $84.1799   $84.18   $84.20   $84.20  
  Purchase #7 $24.64   9.350%   $26.9438   $26.94   $26.95   $26.90  
  7 purchase totals = $875.80       $964.6561   $964.66   $964.70   $964.60