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	$66.48	13.234%	$75.278	$75.28	$75.30	$75.30
Purchase #2	$41.46	10.185%	$45.6827	$45.68	$45.70	$45.70
Purchase #3	$113.33	12.315%	$127.2866	$127.29	$127.30	$127.30
Purchase #4	$106.56	9.416%	$116.5937	$116.59	$116.60	$116.60
Purchase #5	$40.46	5.261%	$42.5886	$42.59	$42.60	$42.60
Purchase #6	$45.94	9.737%	$50.4132	$50.41	$50.40	$50.40
Purchase #7	$126.70	9.123%	$138.2588	$138.26	$138.25	$138.30
7 purchase totals =	$540.93		$596.1016	$596.10	$596.15	$596.20