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	$147.33	13.829%	$167.7043	$167.70	$167.70	$167.70
Purchase #2	$54.50	13.436%	$61.8226	$61.82	$61.80	$61.80
Purchase #3	$122.29	7.375%	$131.3089	$131.31	$131.30	$131.30
Purchase #4	$16.56	5.537%	$17.4769	$17.48	$17.50	$17.50
Purchase #5	$37.96	10.756%	$42.043	$42.04	$42.05	$42.00
Purchase #6	$137.69	13.174%	$155.8293	$155.83	$155.85	$155.80
Purchase #7	$44.35	5.579%	$46.8243	$46.82	$46.80	$46.80
7 purchase totals =	$560.68		$623.0093	$623.00	$623.00	$622.90