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	$140.32	6.340%	$149.2163	$149.22	$149.20	$149.20
Purchase #2	$36.49	8.181%	$39.4752	$39.48	$39.50	$39.50
Purchase #3	$134.44	12.714%	$151.5327	$151.53	$151.55	$151.50
Purchase #4	$154.83	11.538%	$172.6943	$172.69	$172.70	$172.70
Purchase #5	$73.74	11.395%	$82.1427	$82.14	$82.15	$82.10
Purchase #6	$164.40	10.138%	$181.0669	$181.07	$181.05	$181.10
Purchase #7	$217.39	10.191%	$239.5442	$239.54	$239.55	$239.50
7 purchase totals =	$921.61		$1,015.6723	$1,015.67	$1,015.70	$1,015.60