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	$224.99	13.732%	$255.8856	$255.89	$255.90	$255.90
Purchase #2	$132.25	10.558%	$146.213	$146.21	$146.20	$146.20
Purchase #3	$223.84	9.531%	$245.1742	$245.17	$245.15	$245.20
Purchase #4	$228.80	8.293%	$247.7744	$247.77	$247.75	$247.80
Purchase #5	$39.89	13.671%	$45.3434	$45.34	$45.35	$45.30
Purchase #6	$94.48	8.745%	$102.7423	$102.74	$102.75	$102.70
Purchase #7	$91.92	13.623%	$104.4423	$104.44	$104.45	$104.40
7 purchase totals =	$1,036.17		$1,147.5752	$1,147.56	$1,147.55	$1,147.50