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	$17.93	4.207%	$18.6843	$18.68	$18.70	$18.70
Purchase #2	$98.27	13.588%	$111.6229	$111.62	$111.60	$111.60
Purchase #3	$102.27	3.251%	$105.5948	$105.59	$105.60	$105.60
Purchase #4	$180.98	7.687%	$194.8919	$194.89	$194.90	$194.90
Purchase #5	$211.78	10.742%	$234.5294	$234.53	$234.55	$234.50
Purchase #6	$227.95	7.427%	$244.8798	$244.88	$244.90	$244.90
Purchase #7	$165.83	3.742%	$172.0354	$172.04	$172.05	$172.00
7 purchase totals =	$1,005.01		$1,082.2385	$1,082.23	$1,082.30	$1,082.20