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	$99.35	10.648%	$109.9288	$109.93	$109.95	$109.90
Purchase #2	$123.82	6.644%	$132.0466	$132.05	$132.05	$132.00
Purchase #3	$40.54	11.127%	$45.0509	$45.05	$45.05	$45.10
Purchase #4	$144.86	4.140%	$150.8572	$150.86	$150.85	$150.90
Purchase #5	$156.88	7.218%	$168.2036	$168.20	$168.20	$168.20
Purchase #6	$122.59	13.127%	$138.6824	$138.68	$138.70	$138.70
Purchase #7	$105.61	5.793%	$111.728	$111.73	$111.75	$111.70
7 purchase totals =	$793.65		$856.4975	$856.50	$856.55	$856.50