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	$77.88	7.536%	$83.749	$83.75	$83.75	$83.70
Purchase #2	$91.37	8.830%	$99.438	$99.44	$99.45	$99.40
Purchase #3	$25.41	12.429%	$28.5682	$28.57	$28.55	$28.60
Purchase #4	$37.37	5.103%	$39.277	$39.28	$39.30	$39.30
Purchase #5	$238.90	3.838%	$248.069	$248.07	$248.05	$248.10
Purchase #6	$199.37	9.483%	$218.2763	$218.28	$218.30	$218.30
Purchase #7	$80.91	10.137%	$89.1118	$89.11	$89.10	$89.10
7 purchase totals =	$751.21		$806.4893	$806.50	$806.50	$806.50