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	$33.72	13.861%	$38.3939	$38.39	$38.40	$38.40
Purchase #2	$51.25	12.589%	$57.7019	$57.70	$57.70	$57.70
Purchase #3	$99.33	10.294%	$109.555	$109.56	$109.55	$109.60
Purchase #4	$219.59	11.850%	$245.6114	$245.61	$245.60	$245.60
Purchase #5	$57.49	10.406%	$63.4724	$63.47	$63.45	$63.50
Purchase #6	$199.86	4.163%	$208.1802	$208.18	$208.20	$208.20
Purchase #7	$73.62	8.845%	$80.1317	$80.13	$80.15	$80.10
7 purchase totals =	$734.86		$803.0465	$803.04	$803.05	$803.10