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 $20.76   13.646%   $23.5929   $23.59   $23.60   $23.60  
  Purchase #2 $42.99   13.127%   $48.6333   $48.63   $48.65   $48.60  
  Purchase #3 $105.59   7.365%   $113.3667   $113.37   $113.35   $113.40  
  Purchase #4 $223.80   10.245%   $246.7283   $246.73   $246.75   $246.70  
  Purchase #5 $243.39   11.734%   $271.9494   $271.95   $271.95   $271.90  
  Purchase #6 $105.96   5.721%   $112.022   $112.02   $112.00   $112.00  
  Purchase #7 $73.62   12.234%   $82.6267   $82.63   $82.65   $82.60  
  7 purchase totals = $816.11       $898.9193   $898.92   $898.95   $898.80