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	$19.54	5.715%	$20.6567	$20.66	$20.65	$20.70
Purchase #2	$178.86	6.585%	$190.6379	$190.64	$190.65	$190.60
Purchase #3	$116.99	5.664%	$123.6163	$123.62	$123.60	$123.60
Purchase #4	$51.44	6.258%	$54.6591	$54.66	$54.65	$54.70
Purchase #5	$235.86	3.227%	$243.4712	$243.47	$243.45	$243.50
Purchase #6	$73.57	11.802%	$82.2527	$82.25	$82.25	$82.30
Purchase #7	$172.65	5.283%	$181.7711	$181.77	$181.75	$181.80
7 purchase totals =	$848.91		$897.0650	$897.07	$897.00	$897.20