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	$105.75	8.160%	$114.3792	$114.38	$114.40	$114.40
Purchase #2	$130.52	12.272%	$146.5374	$146.54	$146.55	$146.50
Purchase #3	$123.73	13.369%	$140.2715	$140.27	$140.25	$140.30
Purchase #4	$64.51	3.817%	$66.9723	$66.97	$66.95	$67.00
Purchase #5	$19.91	4.604%	$20.8267	$20.83	$20.85	$20.80
Purchase #6	$30.83	12.270%	$34.6128	$34.61	$34.60	$34.60
Purchase #7	$83.85	9.669%	$91.9575	$91.96	$91.95	$92.00
7 purchase totals =	$559.10		$615.5574	$615.56	$615.55	$615.60