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	$207.81	6.162%	$220.6153	$220.62	$220.60	$220.60
Purchase #2	$69.69	10.176%	$76.7817	$76.78	$76.80	$76.80
Purchase #3	$162.66	4.216%	$169.5177	$169.52	$169.50	$169.50
Purchase #4	$52.72	10.200%	$58.0974	$58.10	$58.10	$58.10
Purchase #5	$33.55	10.682%	$37.1338	$37.13	$37.15	$37.10
Purchase #6	$56.47	9.239%	$61.6873	$61.69	$61.70	$61.70
Purchase #7	$38.77	8.640%	$42.1197	$42.12	$42.10	$42.10
7 purchase totals =	$621.67		$665.9529	$665.96	$665.95	$665.90