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	$108.50	7.864%	$117.0324	$117.03	$117.05	$117.00
Purchase #2	$83.50	8.781%	$90.8321	$90.83	$90.85	$90.80
Purchase #3	$143.54	10.666%	$158.85	$158.85	$158.85	$158.90
Purchase #4	$83.31	7.232%	$89.335	$89.34	$89.35	$89.30
Purchase #5	$181.98	13.814%	$207.1187	$207.12	$207.10	$207.10
Purchase #6	$27.53	10.472%	$30.4129	$30.41	$30.40	$30.40
Purchase #7	$228.37	7.111%	$244.6094	$244.61	$244.60	$244.60
7 purchase totals =	$856.73		$938.1905	$938.19	$938.20	$938.10