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	$36.51	10.702%	$40.4173	$40.42	$40.40	$40.40
Purchase #2	$67.84	12.251%	$76.1511	$76.15	$76.15	$76.20
Purchase #3	$170.53	8.440%	$184.9227	$184.92	$184.90	$184.90
Purchase #4	$139.45	3.267%	$144.0058	$144.01	$144.00	$144.00
Purchase #5	$199.47	9.802%	$219.022	$219.02	$219.00	$219.00
Purchase #6	$72.71	13.372%	$82.4328	$82.43	$82.45	$82.40
Purchase #7	$192.85	11.194%	$214.4376	$214.44	$214.45	$214.40
7 purchase totals =	$879.36		$961.3893	$961.39	$961.35	$961.30