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 $227.61   11.559%   $253.9194   $253.92   $253.90   $253.90  
  Purchase #2 $56.89   6.258%   $60.4502   $60.45   $60.45   $60.50  
  Purchase #3 $70.58   3.378%   $72.9642   $72.96   $72.95   $73.00  
  Purchase #4 $93.35   4.108%   $97.1848   $97.18   $97.20   $97.20  
  Purchase #5 $141.67   4.585%   $148.1656   $148.17   $148.15   $148.20  
  Purchase #6 $174.73   5.871%   $184.9884   $184.99   $185.00   $185.00  
  Purchase #7 $88.99   7.341%   $95.5228   $95.52   $95.50   $95.50  
  7 purchase totals = $853.82       $913.1954   $913.19   $913.15   $913.30