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	$37.85	5.267%	$39.8436	$39.84	$39.85	$39.80
Purchase #2	$40.29	7.678%	$43.3835	$43.38	$43.40	$43.40
Purchase #3	$209.33	6.475%	$222.8841	$222.88	$222.90	$222.90
Purchase #4	$83.83	10.503%	$92.6347	$92.63	$92.65	$92.60
Purchase #5	$105.32	5.774%	$111.4012	$111.40	$111.40	$111.40
Purchase #6	$55.77	9.116%	$60.854	$60.85	$60.85	$60.90
Purchase #7	$15.95	8.687%	$17.3356	$17.34	$17.35	$17.30
7 purchase totals =	$548.34		$588.3367	$588.32	$588.40	$588.30