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	$247.98	10.294%	$273.5071	$273.51	$273.50	$273.50
Purchase #2	$150.43	13.840%	$171.2495	$171.25	$171.25	$171.20
Purchase #3	$235.25	12.658%	$265.0279	$265.03	$265.05	$265.00
Purchase #4	$91.25	13.548%	$103.6126	$103.61	$103.60	$103.60
Purchase #5	$157.36	7.357%	$168.937	$168.94	$168.95	$168.90
Purchase #6	$184.29	13.120%	$208.4688	$208.47	$208.45	$208.50
Purchase #7	$237.52	8.106%	$256.7734	$256.77	$256.75	$256.80
7 purchase totals =	$1,304.08		$1,447.5763	$1,447.58	$1,447.55	$1,447.50