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	$42.65	6.455%	$45.4031	$45.40	$45.40	$45.40
Purchase #2	$197.77	3.406%	$204.506	$204.51	$204.50	$204.50
Purchase #3	$173.49	4.529%	$181.3474	$181.35	$181.35	$181.30
Purchase #4	$205.44	8.306%	$222.5038	$222.50	$222.50	$222.50
Purchase #5	$167.52	10.610%	$185.2939	$185.29	$185.30	$185.30
Purchase #6	$105.48	13.145%	$119.3453	$119.35	$119.35	$119.30
Purchase #7	$226.90	11.850%	$253.7877	$253.79	$253.80	$253.80
7 purchase totals =	$1,119.25		$1,212.1872	$1,212.19	$1,212.20	$1,212.10