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	$12.69	3.679%	$13.1569	$13.16	$13.15	$13.20
Purchase #2	$19.31	6.260%	$20.5188	$20.52	$20.50	$20.50
Purchase #3	$103.56	12.133%	$116.1249	$116.12	$116.10	$116.10
Purchase #4	$154.52	11.465%	$172.2357	$172.24	$172.25	$172.20
Purchase #5	$199.26	6.549%	$212.3095	$212.31	$212.30	$212.30
Purchase #6	$72.48	5.749%	$76.6469	$76.65	$76.65	$76.60
Purchase #7	$48.55	4.361%	$50.6673	$50.67	$50.65	$50.70
7 purchase totals =	$610.37		$661.6600	$661.67	$661.60	$661.60