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	$244.29	3.728%	$253.3971	$253.40	$253.40	$253.40
Purchase #2	$116.35	5.364%	$122.591	$122.59	$122.60	$122.60
Purchase #3	$61.49	12.442%	$69.1406	$69.14	$69.15	$69.10
Purchase #4	$247.41	11.488%	$275.8325	$275.83	$275.85	$275.80
Purchase #5	$102.39	10.690%	$113.3355	$113.34	$113.35	$113.30
Purchase #6	$132.35	12.410%	$148.7746	$148.77	$148.75	$148.80
Purchase #7	$91.88	7.191%	$98.4871	$98.49	$98.50	$98.50
7 purchase totals =	$996.16		$1,081.5584	$1,081.56	$1,081.60	$1,081.50