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	$32.64	13.776%	$37.1365	$37.14	$37.15	$37.10
Purchase #2	$85.57	13.146%	$96.819	$96.82	$96.80	$96.80
Purchase #3	$30.60	5.569%	$32.3041	$32.30	$32.30	$32.30
Purchase #4	$129.77	6.132%	$137.7275	$137.73	$137.75	$137.70
Purchase #5	$57.79	5.377%	$60.8974	$60.90	$60.90	$60.90
Purchase #6	$35.40	4.230%	$36.8974	$36.90	$36.90	$36.90
Purchase #7	$19.88	12.505%	$22.366	$22.37	$22.35	$22.40
7 purchase totals =	$391.65		$424.1479	$424.16	$424.15	$424.10