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	$131.87	3.501%	$136.4868	$136.49	$136.50	$136.50
Purchase #2	$193.69	6.592%	$206.458	$206.46	$206.45	$206.50
Purchase #3	$243.52	6.149%	$258.494	$258.49	$258.50	$258.50
Purchase #4	$79.39	3.671%	$82.3044	$82.30	$82.30	$82.30
Purchase #5	$49.65	7.607%	$53.4269	$53.43	$53.45	$53.40
Purchase #6	$41.75	8.871%	$45.4536	$45.45	$45.45	$45.50
Purchase #7	$56.68	9.504%	$62.0669	$62.07	$62.05	$62.10
7 purchase totals =	$796.55		$844.6906	$844.69	$844.70	$844.80