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	$199.54	5.664%	$210.8419	$210.84	$210.85	$210.80
Purchase #2	$148.36	6.847%	$158.5182	$158.52	$158.50	$158.50
Purchase #3	$47.70	12.714%	$53.7646	$53.76	$53.75	$53.80
Purchase #4	$59.81	11.727%	$66.8239	$66.82	$66.80	$66.80
Purchase #5	$125.76	5.695%	$132.922	$132.92	$132.90	$132.90
Purchase #6	$24.96	13.185%	$28.251	$28.25	$28.25	$28.30
Purchase #7	$53.39	7.180%	$57.2234	$57.22	$57.20	$57.20
7 purchase totals =	$659.52		$708.3450	$708.33	$708.25	$708.30