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	$113.89	6.125%	$120.8658	$120.87	$120.85	$120.90
Purchase #2	$9.93	5.662%	$10.4922	$10.49	$10.50	$10.50
Purchase #3	$26.40	12.140%	$29.605	$29.61	$29.60	$29.60
Purchase #4	$67.30	6.753%	$71.8448	$71.84	$71.85	$71.80
Purchase #5	$65.88	9.543%	$72.1669	$72.17	$72.15	$72.20
Purchase #6	$234.34	10.356%	$258.6083	$258.61	$258.60	$258.60
Purchase #7	$78.29	6.190%	$83.1362	$83.14	$83.15	$83.10
7 purchase totals =	$596.03		$646.7192	$646.73	$646.70	$646.70