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	$92.78	6.840%	$99.1262	$99.13	$99.15	$99.10
Purchase #2	$201.45	11.567%	$224.7517	$224.75	$224.75	$224.80
Purchase #3	$6.84	3.392%	$7.072	$7.07	$7.05	$7.10
Purchase #4	$233.97	8.407%	$253.6399	$253.64	$253.65	$253.60
Purchase #5	$167.93	10.254%	$185.1495	$185.15	$185.15	$185.10
Purchase #6	$107.57	3.359%	$111.1833	$111.18	$111.20	$111.20
Purchase #7	$58.25	4.853%	$61.0769	$61.08	$61.10	$61.10
7 purchase totals =	$868.79		$941.9995	$942.00	$942.05	$942.00