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 $59.81   10.433%   $66.05   $66.05   $66.05   $66.10  
  Purchase #2 $76.78   10.539%   $84.8718   $84.87   $84.85   $84.90  
  Purchase #3 $105.93   12.407%   $119.0727   $119.07   $119.05   $119.10  
  Purchase #4 $85.85   9.759%   $94.2281   $94.23   $94.25   $94.20  
  Purchase #5 $150.79   4.195%   $157.1156   $157.12   $157.10   $157.10  
  Purchase #6 $177.66   10.810%   $196.865   $196.87   $196.85   $196.90  
  Purchase #7 $226.48   3.416%   $234.2166   $234.22   $234.20   $234.20  
  7 purchase totals = $883.30       $952.4198   $952.43   $952.35   $952.50