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	$16.73	9.504%	$18.32	$18.32	$18.30	$18.30
Purchase #2	$226.78	13.443%	$257.266	$257.27	$257.25	$257.30
Purchase #3	$67.69	6.615%	$72.1677	$72.17	$72.15	$72.20
Purchase #4	$204.71	8.530%	$222.1718	$222.17	$222.15	$222.20
Purchase #5	$232.69	12.699%	$262.2393	$262.24	$262.25	$262.20
Purchase #6	$178.51	10.644%	$197.5106	$197.51	$197.50	$197.50
Purchase #7	$178.55	6.418%	$190.0093	$190.01	$190.00	$190.00
7 purchase totals =	$1,105.66		$1,219.6847	$1,219.69	$1,219.60	$1,219.70