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	$120.48	9.200%	$131.5642	$131.56	$131.55	$131.60
Purchase #2	$48.55	3.567%	$50.2818	$50.28	$50.30	$50.30
Purchase #3	$102.64	12.195%	$115.1569	$115.16	$115.15	$115.20
Purchase #4	$100.85	10.547%	$111.4866	$111.49	$111.50	$111.50
Purchase #5	$245.81	12.637%	$276.873	$276.87	$276.85	$276.90
Purchase #6	$226.91	5.404%	$239.1722	$239.17	$239.15	$239.20
Purchase #7	$71.48	7.155%	$76.5944	$76.59	$76.60	$76.60
7 purchase totals =	$916.72		$1,001.1291	$1,001.12	$1,001.10	$1,001.30