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	$74.92	11.109%	$83.2429	$83.24	$83.25	$83.20
Purchase #2	$40.90	10.115%	$45.037	$45.04	$45.05	$45.00
Purchase #3	$217.56	7.521%	$233.9227	$233.92	$233.90	$233.90
Purchase #4	$137.95	4.104%	$143.6115	$143.61	$143.60	$143.60
Purchase #5	$186.42	13.861%	$212.2597	$212.26	$212.25	$212.30
Purchase #6	$28.55	4.794%	$29.9187	$29.92	$29.90	$29.90
Purchase #7	$83.39	10.821%	$92.4136	$92.41	$92.40	$92.40
7 purchase totals =	$769.69		$840.4061	$840.40	$840.35	$840.30