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	$54.76	3.508%	$56.681	$56.68	$56.70	$56.70
Purchase #2	$34.91	6.357%	$37.1292	$37.13	$37.15	$37.10
Purchase #3	$177.86	5.123%	$186.9718	$186.97	$186.95	$187.00
Purchase #4	$101.64	5.380%	$107.1082	$107.11	$107.10	$107.10
Purchase #5	$74.27	10.527%	$82.0884	$82.09	$82.10	$82.10
Purchase #6	$134.53	10.132%	$148.1606	$148.16	$148.15	$148.20
Purchase #7	$39.50	6.542%	$42.0841	$42.08	$42.10	$42.10
7 purchase totals =	$617.47		$660.2233	$660.22	$660.25	$660.30