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	$86.74	5.216%	$91.2644	$91.26	$91.25	$91.30
Purchase #2	$91.83	11.754%	$102.6237	$102.62	$102.60	$102.60
Purchase #3	$130.52	10.173%	$143.7978	$143.80	$143.80	$143.80
Purchase #4	$117.90	7.764%	$127.0538	$127.05	$127.05	$127.10
Purchase #5	$192.72	12.752%	$217.2957	$217.30	$217.30	$217.30
Purchase #6	$157.64	8.562%	$171.1371	$171.14	$171.15	$171.10
Purchase #7	$20.25	4.349%	$21.1307	$21.13	$21.15	$21.10
7 purchase totals =	$797.60		$874.3032	$874.30	$874.30	$874.30