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	$138.66	5.740%	$146.6191	$146.62	$146.60	$146.60
Purchase #2	$112.49	4.367%	$117.4024	$117.40	$117.40	$117.40
Purchase #3	$23.72	11.751%	$26.5073	$26.51	$26.50	$26.50
Purchase #4	$81.45	6.215%	$86.5121	$86.51	$86.50	$86.50
Purchase #5	$7.28	9.118%	$7.9438	$7.94	$7.95	$7.90
Purchase #6	$154.92	11.243%	$172.3377	$172.34	$172.35	$172.30
Purchase #7	$212.97	4.755%	$223.0967	$223.10	$223.10	$223.10
7 purchase totals =	$731.49		$780.4191	$780.42	$780.40	$780.30