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	$28.67	13.700%	$32.5978	$32.60	$32.60	$32.60
Purchase #2	$39.25	4.506%	$41.0186	$41.02	$41.00	$41.00
Purchase #3	$234.84	10.120%	$258.6058	$258.61	$258.60	$258.60
Purchase #4	$83.87	5.294%	$88.3101	$88.31	$88.30	$88.30
Purchase #5	$196.39	13.617%	$223.1324	$223.13	$223.15	$223.10
Purchase #6	$48.35	8.350%	$52.3872	$52.39	$52.40	$52.40
Purchase #7	$101.40	7.413%	$108.9168	$108.92	$108.90	$108.90
7 purchase totals =	$732.77		$804.9687	$804.98	$804.95	$804.90