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	$74.33	9.436%	$81.3438	$81.34	$81.35	$81.30
Purchase #2	$191.54	3.436%	$198.1213	$198.12	$198.10	$198.10
Purchase #3	$227.89	7.628%	$245.2734	$245.27	$245.25	$245.30
Purchase #4	$231.93	8.539%	$251.7345	$251.73	$251.75	$251.70
Purchase #5	$209.89	13.456%	$238.1328	$238.13	$238.15	$238.10
Purchase #6	$15.42	11.222%	$17.1504	$17.15	$17.15	$17.20
Purchase #7	$52.89	13.350%	$59.9508	$59.95	$59.95	$60.00
7 purchase totals =	$1,003.89		$1,091.7070	$1,091.69	$1,091.70	$1,091.70