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	$9.90	3.299%	$10.2266	$10.23	$10.25	$10.20
Purchase #2	$105.42	3.722%	$109.3437	$109.34	$109.35	$109.30
Purchase #3	$121.81	13.412%	$138.1472	$138.15	$138.15	$138.10
Purchase #4	$46.37	9.573%	$50.809	$50.81	$50.80	$50.80
Purchase #5	$241.69	13.613%	$274.5913	$274.59	$274.60	$274.60
Purchase #6	$80.70	10.111%	$88.8596	$88.86	$88.85	$88.90
Purchase #7	$119.86	9.418%	$131.1484	$131.15	$131.15	$131.10
7 purchase totals =	$725.75		$803.1258	$803.13	$803.15	$803.00