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	$89.46	11.188%	$99.4688	$99.47	$99.45	$99.50
Purchase #2	$64.44	9.114%	$70.3131	$70.31	$70.30	$70.30
Purchase #3	$47.82	6.474%	$50.9159	$50.92	$50.90	$50.90
Purchase #4	$211.56	6.803%	$225.9524	$225.95	$225.95	$226.00
Purchase #5	$90.81	12.433%	$102.1004	$102.10	$102.10	$102.10
Purchase #6	$61.43	10.265%	$67.7358	$67.74	$67.75	$67.70
Purchase #7	$97.93	10.350%	$108.0658	$108.07	$108.05	$108.10
7 purchase totals =	$663.45		$724.5522	$724.56	$724.50	$724.60