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	$139.27	13.157%	$157.5938	$157.59	$157.60	$157.60
Purchase #2	$156.89	12.361%	$176.2832	$176.28	$176.30	$176.30
Purchase #3	$247.35	9.665%	$271.2564	$271.26	$271.25	$271.30
Purchase #4	$145.35	13.343%	$164.7441	$164.74	$164.75	$164.70
Purchase #5	$27.92	7.385%	$29.9819	$29.98	$30.00	$30.00
Purchase #6	$170.60	8.479%	$185.0652	$185.07	$185.05	$185.10
Purchase #7	$68.63	11.600%	$76.5911	$76.59	$76.60	$76.60
7 purchase totals =	$956.01		$1,061.5157	$1,061.51	$1,061.55	$1,061.60