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	$18.95	6.626%	$20.2056	$20.21	$20.20	$20.20
Purchase #2	$18.90	10.185%	$20.825	$20.83	$20.85	$20.80
Purchase #3	$240.70	11.455%	$268.2722	$268.27	$268.25	$268.30
Purchase #4	$17.39	4.513%	$18.1748	$18.17	$18.15	$18.20
Purchase #5	$133.72	12.308%	$150.1783	$150.18	$150.20	$150.20
Purchase #6	$46.95	8.153%	$50.7778	$50.78	$50.80	$50.80
Purchase #7	$149.63	6.134%	$158.8083	$158.81	$158.80	$158.80
7 purchase totals =	$626.24		$687.2420	$687.25	$687.25	$687.30