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	$80.40	12.353%	$90.3318	$90.33	$90.35	$90.30
Purchase #2	$153.67	7.760%	$165.5948	$165.59	$165.60	$165.60
Purchase #3	$89.46	3.814%	$92.872	$92.87	$92.85	$92.90
Purchase #4	$128.37	4.872%	$134.6242	$134.62	$134.60	$134.60
Purchase #5	$58.36	13.361%	$66.1575	$66.16	$66.15	$66.20
Purchase #6	$53.75	3.250%	$55.4969	$55.50	$55.50	$55.50
Purchase #7	$81.72	4.549%	$85.4374	$85.44	$85.45	$85.40
7 purchase totals =	$645.73		$690.5146	$690.51	$690.50	$690.50