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	$43.49	5.363%	$45.8224	$45.82	$45.80	$45.80
Purchase #2	$203.99	10.613%	$225.6395	$225.64	$225.65	$225.60
Purchase #3	$146.58	12.422%	$164.7882	$164.79	$164.80	$164.80
Purchase #4	$147.53	3.301%	$152.4	$152.40	$152.40	$152.40
Purchase #5	$155.95	5.615%	$164.7066	$164.71	$164.70	$164.70
Purchase #6	$100.30	8.181%	$108.5055	$108.51	$108.50	$108.50
Purchase #7	$209.31	4.655%	$219.0534	$219.05	$219.05	$219.10
7 purchase totals =	$1,007.15		$1,080.9156	$1,080.92	$1,080.90	$1,080.90