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	$37.40	13.172%	$42.3263	$42.33	$42.35	$42.30
Purchase #2	$56.27	12.463%	$63.2829	$63.28	$63.30	$63.30
Purchase #3	$137.33	10.628%	$151.9254	$151.93	$151.95	$151.90
Purchase #4	$211.76	7.784%	$228.2434	$228.24	$228.25	$228.20
Purchase #5	$151.25	4.475%	$158.0184	$158.02	$158.00	$158.00
Purchase #6	$95.53	13.488%	$108.4151	$108.42	$108.40	$108.40
Purchase #7	$215.33	13.340%	$244.055	$244.06	$244.05	$244.10
7 purchase totals =	$904.87		$996.2665	$996.28	$996.30	$996.20