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	$246.63	12.815%	$278.2356	$278.24	$278.25	$278.20
Purchase #2	$133.64	13.306%	$151.4221	$151.42	$151.40	$151.40
Purchase #3	$69.98	13.630%	$79.5183	$79.52	$79.50	$79.50
Purchase #4	$212.31	8.179%	$229.6748	$229.67	$229.65	$229.70
Purchase #5	$214.61	4.281%	$223.7975	$223.80	$223.80	$223.80
Purchase #6	$96.26	8.462%	$104.4055	$104.41	$104.40	$104.40
Purchase #7	$30.83	7.520%	$33.1484	$33.15	$33.15	$33.10
7 purchase totals =	$1,004.26		$1,100.2022	$1,100.21	$1,100.15	$1,100.10