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	$112.31	13.777%	$127.7829	$127.78	$127.80	$127.80
Purchase #2	$167.40	12.511%	$188.3434	$188.34	$188.35	$188.30
Purchase #3	$157.50	11.263%	$175.2392	$175.24	$175.25	$175.20
Purchase #4	$223.68	12.289%	$251.168	$251.17	$251.15	$251.20
Purchase #5	$144.69	6.556%	$154.1759	$154.18	$154.20	$154.20
Purchase #6	$34.32	8.261%	$37.1552	$37.16	$37.15	$37.20
Purchase #7	$34.35	8.547%	$37.2859	$37.29	$37.30	$37.30
7 purchase totals =	$874.25		$971.1505	$971.16	$971.20	$971.20