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	$159.45	4.302%	$166.3095	$166.31	$166.30	$166.30
Purchase #2	$41.66	9.809%	$45.7464	$45.75	$45.75	$45.70
Purchase #3	$117.58	5.468%	$124.0093	$124.01	$124.00	$124.00
Purchase #4	$248.32	11.609%	$277.1475	$277.15	$277.15	$277.10
Purchase #5	$67.27	6.238%	$71.4663	$71.47	$71.45	$71.50
Purchase #6	$234.52	7.362%	$251.7854	$251.79	$251.80	$251.80
Purchase #7	$95.79	9.175%	$104.5787	$104.58	$104.60	$104.60
7 purchase totals =	$964.59		$1,041.0431	$1,041.06	$1,041.05	$1,041.00