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	$63.71	3.314%	$65.8213	$65.82	$65.80	$65.80
Purchase #2	$239.71	4.800%	$251.2161	$251.22	$251.20	$251.20
Purchase #3	$73.26	10.253%	$80.7713	$80.77	$80.75	$80.80
Purchase #4	$49.79	13.652%	$56.5873	$56.59	$56.60	$56.60
Purchase #5	$50.80	6.384%	$54.0431	$54.04	$54.05	$54.00
Purchase #6	$211.45	12.790%	$238.4945	$238.49	$238.50	$238.50
Purchase #7	$34.87	6.807%	$37.2436	$37.24	$37.25	$37.20
7 purchase totals =	$723.59		$784.1772	$784.17	$784.15	$784.10