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	$160.77	4.861%	$168.585	$168.59	$168.60	$168.60
Purchase #2	$192.46	12.445%	$216.4116	$216.41	$216.40	$216.40
Purchase #3	$134.50	3.630%	$139.3824	$139.38	$139.40	$139.40
Purchase #4	$35.41	6.561%	$37.7333	$37.73	$37.75	$37.70
Purchase #5	$29.94	12.168%	$33.5831	$33.58	$33.60	$33.60
Purchase #6	$74.38	9.609%	$81.5272	$81.53	$81.55	$81.50
Purchase #7	$136.99	6.622%	$146.0615	$146.06	$146.05	$146.10
7 purchase totals =	$764.45		$823.2841	$823.28	$823.35	$823.30