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	$33.56	11.222%	$37.3261	$37.33	$37.35	$37.30
Purchase #2	$99.66	3.602%	$103.2498	$103.25	$103.25	$103.20
Purchase #3	$137.67	9.205%	$150.3425	$150.34	$150.35	$150.30
Purchase #4	$199.51	7.416%	$214.3057	$214.31	$214.30	$214.30
Purchase #5	$118.89	12.856%	$134.1745	$134.17	$134.15	$134.20
Purchase #6	$48.74	9.732%	$53.4834	$53.48	$53.50	$53.50
Purchase #7	$116.44	6.325%	$123.8048	$123.80	$123.80	$123.80
7 purchase totals =	$754.47		$816.6868	$816.68	$816.70	$816.60