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	$16.51	9.733%	$18.1169	$18.12	$18.10	$18.10
Purchase #2	$91.54	4.244%	$95.425	$95.43	$95.45	$95.40
Purchase #3	$245.76	8.696%	$267.1313	$267.13	$267.15	$267.10
Purchase #4	$239.93	9.734%	$263.2848	$263.28	$263.30	$263.30
Purchase #5	$37.35	11.865%	$41.7816	$41.78	$41.80	$41.80
Purchase #6	$73.76	12.346%	$82.8664	$82.87	$82.85	$82.90
Purchase #7	$107.91	3.377%	$111.5541	$111.55	$111.55	$111.60
7 purchase totals =	$812.76		$880.1601	$880.16	$880.20	$880.20