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	$17.35	5.118%	$18.238	$18.24	$18.25	$18.20
Purchase #2	$113.35	10.189%	$124.8992	$124.90	$124.90	$124.90
Purchase #3	$81.25	11.353%	$90.4743	$90.47	$90.45	$90.50
Purchase #4	$218.79	8.843%	$238.1376	$238.14	$238.15	$238.10
Purchase #5	$160.43	3.330%	$165.7723	$165.77	$165.75	$165.80
Purchase #6	$203.47	12.823%	$229.561	$229.56	$229.55	$229.60
Purchase #7	$196.40	12.689%	$221.3212	$221.32	$221.30	$221.30
7 purchase totals =	$991.04		$1,088.4036	$1,088.40	$1,088.35	$1,088.40