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 $46.91   4.365%   $48.9576   $48.96   $48.95   $49.00  
  Purchase #2 $143.37   8.269%   $155.2253   $155.23   $155.25   $155.20  
  Purchase #3 $226.95   8.218%   $245.6008   $245.60   $245.60   $245.60  
  Purchase #4 $210.83   3.782%   $218.8036   $218.80   $218.80   $218.80  
  Purchase #5 $206.63   6.873%   $220.8317   $220.83   $220.85   $220.80  
  Purchase #6 $10.86   10.557%   $12.0065   $12.01   $12.00   $12.00  
  Purchase #7 $88.42   4.291%   $92.2141   $92.21   $92.20   $92.20  
  7 purchase totals = $933.97       $993.6396   $993.64   $993.65   $993.60