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	$166.77	13.234%	$188.8403	$188.84	$188.85	$188.80
Purchase #2	$146.56	6.228%	$155.6878	$155.69	$155.70	$155.70
Purchase #3	$160.94	7.205%	$172.5357	$172.54	$172.55	$172.50
Purchase #4	$157.47	11.120%	$174.9807	$174.98	$175.00	$175.00
Purchase #5	$11.53	11.838%	$12.8949	$12.89	$12.90	$12.90
Purchase #6	$142.29	3.842%	$147.7568	$147.76	$147.75	$147.80
Purchase #7	$247.64	12.790%	$279.3132	$279.31	$279.30	$279.30
7 purchase totals =	$1,033.20		$1,132.0094	$1,132.01	$1,132.05	$1,132.00