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	$20.83	13.740%	$23.692	$23.69	$23.70	$23.70
Purchase #2	$150.64	10.230%	$166.0505	$166.05	$166.05	$166.10
Purchase #3	$17.55	4.481%	$18.3364	$18.34	$18.35	$18.30
Purchase #4	$243.64	11.491%	$271.6367	$271.64	$271.65	$271.60
Purchase #5	$8.80	13.857%	$10.0194	$10.02	$10.00	$10.00
Purchase #6	$53.57	3.136%	$55.25	$55.25	$55.25	$55.30
Purchase #7	$244.50	4.253%	$254.8986	$254.90	$254.90	$254.90
7 purchase totals =	$739.53		$799.8836	$799.89	$799.90	$799.90