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	$221.68	4.618%	$231.9172	$231.92	$231.90	$231.90
Purchase #2	$45.79	9.287%	$50.0425	$50.04	$50.05	$50.00
Purchase #3	$161.32	6.701%	$172.1301	$172.13	$172.15	$172.10
Purchase #4	$173.50	13.331%	$196.6293	$196.63	$196.65	$196.60
Purchase #5	$140.83	9.367%	$154.0215	$154.02	$154.00	$154.00
Purchase #6	$78.27	6.458%	$83.3247	$83.32	$83.30	$83.30
Purchase #7	$8.55	12.263%	$9.5985	$9.60	$9.60	$9.60
7 purchase totals =	$829.94		$897.6638	$897.66	$897.65	$897.50