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	$103.96	12.304%	$116.7512	$116.75	$116.75	$116.80
Purchase #2	$132.27	8.268%	$143.2061	$143.21	$143.20	$143.20
Purchase #3	$99.37	6.171%	$105.5021	$105.50	$105.50	$105.50
Purchase #4	$214.91	13.220%	$243.3211	$243.32	$243.30	$243.30
Purchase #5	$14.49	8.572%	$15.7321	$15.73	$15.75	$15.70
Purchase #6	$224.79	11.131%	$249.8114	$249.81	$249.80	$249.80
Purchase #7	$35.72	4.369%	$37.2806	$37.28	$37.30	$37.30
7 purchase totals =	$825.51		$911.6046	$911.60	$911.60	$911.60