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	$12.90	4.121%	$13.4316	$13.43	$13.45	$13.40
Purchase #2	$58.61	9.586%	$64.2284	$64.23	$64.25	$64.20
Purchase #3	$222.90	5.184%	$234.4551	$234.46	$234.45	$234.50
Purchase #4	$212.84	13.258%	$241.0583	$241.06	$241.05	$241.10
Purchase #5	$9.50	10.753%	$10.5215	$10.52	$10.50	$10.50
Purchase #6	$28.92	11.633%	$32.2843	$32.28	$32.30	$32.30
Purchase #7	$102.70	11.849%	$114.8689	$114.87	$114.85	$114.90
7 purchase totals =	$648.37		$710.8481	$710.85	$710.85	$710.90