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	$123.86	11.549%	$138.1646	$138.16	$138.15	$138.20
Purchase #2	$19.27	6.499%	$20.5224	$20.52	$20.50	$20.50
Purchase #3	$245.80	7.130%	$263.3255	$263.33	$263.35	$263.30
Purchase #4	$236.95	11.211%	$263.5145	$263.51	$263.50	$263.50
Purchase #5	$175.77	7.674%	$189.2586	$189.26	$189.25	$189.30
Purchase #6	$99.73	11.622%	$111.3206	$111.32	$111.30	$111.30
Purchase #7	$135.35	4.346%	$141.2323	$141.23	$141.25	$141.20
7 purchase totals =	$1,036.73		$1,127.3385	$1,127.33	$1,127.30	$1,127.30