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	$37.77	12.431%	$42.4652	$42.47	$42.45	$42.50
Purchase #2	$240.55	3.469%	$248.8947	$248.89	$248.90	$248.90
Purchase #3	$105.61	8.408%	$114.4897	$114.49	$114.50	$114.50
Purchase #4	$161.72	13.847%	$184.1134	$184.11	$184.10	$184.10
Purchase #5	$108.74	8.330%	$117.798	$117.80	$117.80	$117.80
Purchase #6	$95.65	10.317%	$105.5182	$105.52	$105.50	$105.50
Purchase #7	$143.63	7.449%	$154.329	$154.33	$154.35	$154.30
7 purchase totals =	$893.67		$967.6082	$967.61	$967.60	$967.60