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	$12.60	10.454%	$13.9172	$13.92	$13.90	$13.90
Purchase #2	$23.78	11.590%	$26.5361	$26.54	$26.55	$26.50
Purchase #3	$33.66	11.593%	$37.5622	$37.56	$37.55	$37.60
Purchase #4	$146.49	10.254%	$161.5111	$161.51	$161.50	$161.50
Purchase #5	$238.82	6.468%	$254.2669	$254.27	$254.25	$254.30
Purchase #6	$29.85	12.136%	$33.4726	$33.47	$33.45	$33.50
Purchase #7	$249.51	4.703%	$261.2445	$261.24	$261.25	$261.20
7 purchase totals =	$734.71		$788.5106	$788.51	$788.45	$788.50