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	$35.94	7.288%	$38.5593	$38.56	$38.55	$38.60
Purchase #2	$87.77	7.278%	$94.1579	$94.16	$94.15	$94.20
Purchase #3	$92.38	13.624%	$104.9659	$104.97	$104.95	$105.00
Purchase #4	$244.30	10.682%	$270.3961	$270.40	$270.40	$270.40
Purchase #5	$151.75	9.130%	$165.6048	$165.60	$165.60	$165.60
Purchase #6	$75.72	7.172%	$81.1506	$81.15	$81.15	$81.20
Purchase #7	$93.51	10.488%	$103.3173	$103.32	$103.30	$103.30
7 purchase totals =	$781.37		$858.1519	$858.16	$858.10	$858.30