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	$72.26	8.834%	$78.6434	$78.64	$78.65	$78.60
Purchase #2	$136.49	5.362%	$143.8086	$143.81	$143.80	$143.80
Purchase #3	$76.96	7.517%	$82.7451	$82.75	$82.75	$82.70
Purchase #4	$25.55	11.377%	$28.4568	$28.46	$28.45	$28.50
Purchase #5	$42.79	3.677%	$44.3634	$44.36	$44.35	$44.40
Purchase #6	$32.56	5.355%	$34.3036	$34.30	$34.30	$34.30
Purchase #7	$225.92	12.462%	$254.0742	$254.07	$254.05	$254.10
7 purchase totals =	$612.53		$666.3951	$666.39	$666.35	$666.40