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	$99.75	3.499%	$103.2403	$103.24	$103.25	$103.20
Purchase #2	$146.96	9.804%	$161.368	$161.37	$161.35	$161.40
Purchase #3	$153.54	7.398%	$164.8989	$164.90	$164.90	$164.90
Purchase #4	$155.25	13.607%	$176.3749	$176.37	$176.35	$176.40
Purchase #5	$29.51	5.395%	$31.1021	$31.10	$31.10	$31.10
Purchase #6	$17.56	11.411%	$19.5638	$19.56	$19.55	$19.60
Purchase #7	$53.59	5.843%	$56.7213	$56.72	$56.70	$56.70
7 purchase totals =	$656.16		$713.2693	$713.26	$713.20	$713.30