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	$37.69	11.723%	$42.1084	$42.11	$42.10	$42.10
Purchase #2	$205.63	4.221%	$214.3096	$214.31	$214.30	$214.30
Purchase #3	$58.27	10.671%	$64.488	$64.49	$64.50	$64.50
Purchase #4	$220.88	3.649%	$228.9399	$228.94	$228.95	$228.90
Purchase #5	$182.57	9.285%	$199.5216	$199.52	$199.50	$199.50
Purchase #6	$158.40	4.367%	$165.3173	$165.32	$165.30	$165.30
Purchase #7	$32.61	6.143%	$34.6132	$34.61	$34.60	$34.60
7 purchase totals =	$896.05		$949.2980	$949.30	$949.25	$949.20