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	$41.33	13.216%	$46.7922	$46.79	$46.80	$46.80
Purchase #2	$209.43	12.456%	$235.5166	$235.52	$235.50	$235.50
Purchase #3	$169.42	6.610%	$180.6187	$180.62	$180.60	$180.60
Purchase #4	$233.51	7.238%	$250.4115	$250.41	$250.40	$250.40
Purchase #5	$240.76	7.532%	$258.894	$258.89	$258.90	$258.90
Purchase #6	$101.85	3.353%	$105.265	$105.27	$105.25	$105.30
Purchase #7	$228.65	4.109%	$238.0452	$238.05	$238.05	$238.00
7 purchase totals =	$1,224.95		$1,315.5432	$1,315.55	$1,315.50	$1,315.50