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	$13.64	11.300%	$15.1813	$15.18	$15.20	$15.20
Purchase #2	$212.33	5.362%	$223.7151	$223.72	$223.70	$223.70
Purchase #3	$146.65	8.473%	$159.0757	$159.08	$159.10	$159.10
Purchase #4	$82.25	11.160%	$91.4291	$91.43	$91.45	$91.40
Purchase #5	$180.41	10.403%	$199.1781	$199.18	$199.20	$199.20
Purchase #6	$241.43	7.497%	$259.53	$259.53	$259.55	$259.50
Purchase #7	$148.76	4.491%	$155.4408	$155.44	$155.45	$155.40
7 purchase totals =	$1,025.47		$1,103.5501	$1,103.56	$1,103.65	$1,103.50