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	$126.67	3.730%	$131.3948	$131.39	$131.40	$131.40
Purchase #2	$118.81	11.636%	$132.6347	$132.63	$132.65	$132.60
Purchase #3	$23.41	10.760%	$25.9289	$25.93	$25.95	$25.90
Purchase #4	$11.46	9.522%	$12.5512	$12.55	$12.55	$12.60
Purchase #5	$63.52	5.759%	$67.1781	$67.18	$67.20	$67.20
Purchase #6	$36.39	4.104%	$37.8834	$37.88	$37.90	$37.90
Purchase #7	$98.76	13.278%	$111.8734	$111.87	$111.85	$111.90
7 purchase totals =	$479.02		$519.4445	$519.43	$519.50	$519.50