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	$85.79	13.259%	$97.1649	$97.16	$97.15	$97.20
Purchase #2	$54.76	9.384%	$59.8987	$59.90	$59.90	$59.90
Purchase #3	$234.89	10.129%	$258.682	$258.68	$258.70	$258.70
Purchase #4	$104.76	5.362%	$110.3772	$110.38	$110.40	$110.40
Purchase #5	$56.27	9.337%	$61.5239	$61.52	$61.50	$61.50
Purchase #6	$97.71	10.571%	$108.0389	$108.04	$108.05	$108.00
Purchase #7	$118.32	9.545%	$129.6136	$129.61	$129.60	$129.60
7 purchase totals =	$752.50		$825.2992	$825.29	$825.30	$825.30