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 $231.78   13.577%   $263.2488   $263.25   $263.25   $263.20  
  Purchase #2 $122.26   3.472%   $126.5049   $126.50   $126.50   $126.50  
  Purchase #3 $12.65   5.696%   $13.3705   $13.37   $13.35   $13.40  
  Purchase #4 $124.68   9.813%   $136.9148   $136.91   $136.90   $136.90  
  Purchase #5 $84.98   12.638%   $95.7198   $95.72   $95.70   $95.70  
  Purchase #6 $154.27   9.143%   $168.3749   $168.37   $168.35   $168.40  
  Purchase #7 $138.56   7.185%   $148.5155   $148.52   $148.50   $148.50  
  7 purchase totals = $869.18       $952.6492   $952.64   $952.55   $952.60