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	$79.45	8.660%	$86.3304	$86.33	$86.35	$86.30
Purchase #2	$36.77	12.378%	$41.3214	$41.32	$41.30	$41.30
Purchase #3	$245.41	4.262%	$255.8694	$255.87	$255.85	$255.90
Purchase #4	$110.60	9.847%	$121.4908	$121.49	$121.50	$121.50
Purchase #5	$60.29	3.324%	$62.294	$62.29	$62.30	$62.30
Purchase #6	$123.58	12.574%	$139.1189	$139.12	$139.10	$139.10
Purchase #7	$139.31	5.413%	$146.8509	$146.85	$146.85	$146.90
7 purchase totals =	$795.41		$853.2758	$853.27	$853.25	$853.30