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	$88.47	3.223%	$91.3214	$91.32	$91.30	$91.30
Purchase #2	$26.38	8.512%	$28.6255	$28.63	$28.65	$28.60
Purchase #3	$14.66	3.753%	$15.2102	$15.21	$15.20	$15.20
Purchase #4	$207.71	6.746%	$221.7221	$221.72	$221.70	$221.70
Purchase #5	$24.28	11.828%	$27.1518	$27.15	$27.15	$27.20
Purchase #6	$137.73	13.477%	$156.2919	$156.29	$156.30	$156.30
Purchase #7	$89.27	12.124%	$100.0931	$100.09	$100.10	$100.10
7 purchase totals =	$588.50		$640.4160	$640.41	$640.40	$640.40