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 $94.57   9.461%   $103.5173   $103.52   $103.50   $103.50  
  Purchase #2 $66.32   6.300%   $70.4982   $70.50   $70.50   $70.50  
  Purchase #3 $123.96   8.648%   $134.6801   $134.68   $134.70   $134.70  
  Purchase #4 $83.82   9.426%   $91.7209   $91.72   $91.70   $91.70  
  Purchase #5 $213.30   11.562%   $237.9617   $237.96   $237.95   $238.00  
  Purchase #6 $66.90   13.663%   $76.0405   $76.04   $76.05   $76.00  
  Purchase #7 $141.47   4.804%   $148.2662   $148.27   $148.25   $148.30  
  7 purchase totals = $790.34       $862.6849   $862.69   $862.65   $862.70