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	$158.77	13.620%	$180.3945	$180.39	$180.40	$180.40
Purchase #2	$150.56	7.563%	$161.9469	$161.95	$161.95	$161.90
Purchase #3	$148.41	11.559%	$165.5647	$165.56	$165.55	$165.60
Purchase #4	$122.85	12.420%	$138.108	$138.11	$138.10	$138.10
Purchase #5	$72.89	7.176%	$78.1206	$78.12	$78.10	$78.10
Purchase #6	$78.90	4.385%	$82.3598	$82.36	$82.35	$82.40
Purchase #7	$204.92	13.683%	$232.9592	$232.96	$232.95	$233.00
7 purchase totals =	$937.30		$1,039.4537	$1,039.45	$1,039.40	$1,039.50