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 $61.41   5.724%   $64.9251   $64.93   $64.95   $64.90  
  Purchase #2 $188.97   3.689%   $195.9411   $195.94   $195.95   $195.90  
  Purchase #3 $20.63   8.332%   $22.3489   $22.35   $22.35   $22.30  
  Purchase #4 $209.84   5.321%   $221.0056   $221.01   $221.00   $221.00  
  Purchase #5 $46.86   4.331%   $48.8895   $48.89   $48.90   $48.90  
  Purchase #6 $182.97   3.533%   $189.4343   $189.43   $189.45   $189.40  
  Purchase #7 $134.39   12.670%   $151.4172   $151.42   $151.40   $151.40  
  7 purchase totals = $845.07       $893.9617   $893.97   $894.00   $893.80