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	$64.75	9.805%	$71.0987	$71.10	$71.10	$71.10
Purchase #2	$152.80	3.786%	$158.585	$158.59	$158.60	$158.60
Purchase #3	$82.53	4.190%	$85.988	$85.99	$86.00	$86.00
Purchase #4	$33.74	11.822%	$37.7287	$37.73	$37.75	$37.70
Purchase #5	$155.59	10.694%	$172.2288	$172.23	$172.25	$172.20
Purchase #6	$77.74	7.277%	$83.3971	$83.40	$83.40	$83.40
Purchase #7	$184.32	9.285%	$201.4341	$201.43	$201.45	$201.40
7 purchase totals =	$751.47		$810.4604	$810.47	$810.55	$810.40