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	$106.64	10.782%	$118.1379	$118.14	$118.15	$118.10
Purchase #2	$95.28	10.277%	$105.0719	$105.07	$105.05	$105.10
Purchase #3	$129.60	7.219%	$138.9558	$138.96	$138.95	$139.00
Purchase #4	$27.35	13.869%	$31.1432	$31.14	$31.15	$31.10
Purchase #5	$132.32	7.607%	$142.3856	$142.39	$142.40	$142.40
Purchase #6	$129.95	12.824%	$146.6148	$146.61	$146.60	$146.60
Purchase #7	$105.52	4.830%	$110.6166	$110.62	$110.60	$110.60
7 purchase totals =	$726.66		$792.9258	$792.93	$792.90	$792.90