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 $60.46   6.154%   $64.1807   $64.18   $64.20   $64.20  
  Purchase #2 $248.57   7.521%   $267.2649   $267.26   $267.25   $267.30  
  Purchase #3 $69.70   3.166%   $71.9067   $71.91   $71.90   $71.90  
  Purchase #4 $143.61   9.781%   $157.6565   $157.66   $157.65   $157.70  
  Purchase #5 $215.73   8.655%   $234.4014   $234.40   $234.40   $234.40  
  Purchase #6 $85.35   3.689%   $88.4986   $88.50   $88.50   $88.50  
  Purchase #7 $42.76   9.463%   $46.8064   $46.81   $46.80   $46.80  
  7 purchase totals = $866.18       $930.7152   $930.72   $930.70   $930.80