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	$30.42	9.701%	$33.371	$33.37	$33.35	$33.40
Purchase #2	$229.87	10.301%	$253.5489	$253.55	$253.55	$253.50
Purchase #3	$68.90	6.443%	$73.3392	$73.34	$73.35	$73.30
Purchase #4	$223.99	12.325%	$251.5968	$251.60	$251.60	$251.60
Purchase #5	$62.92	12.818%	$70.9851	$70.99	$71.00	$71.00
Purchase #6	$160.64	5.136%	$168.8905	$168.89	$168.90	$168.90
Purchase #7	$137.33	4.236%	$143.1473	$143.15	$143.15	$143.10
7 purchase totals =	$914.07		$994.8788	$994.89	$994.90	$994.80