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 $57.48   7.203%   $61.6203   $61.62   $61.60   $61.60  
  Purchase #2 $151.60   12.649%   $170.7759   $170.78   $170.80   $170.80  
  Purchase #3 $95.64   3.734%   $99.2112   $99.21   $99.20   $99.20  
  Purchase #4 $66.71   10.778%   $73.9   $73.90   $73.90   $73.90  
  Purchase #5 $54.53   13.642%   $61.969   $61.97   $61.95   $62.00  
  Purchase #6 $12.50   11.491%   $13.9364   $13.94   $13.95   $13.90  
  Purchase #7 $23.69   12.260%   $26.5944   $26.59   $26.60   $26.60  
  7 purchase totals = $462.15       $508.0072   $508.01   $508.00   $508.00