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	$18.73	10.827%	$20.7579	$20.76	$20.75	$20.80
Purchase #2	$50.79	7.320%	$54.5078	$54.51	$54.50	$54.50
Purchase #3	$199.34	11.149%	$221.5644	$221.56	$221.55	$221.60
Purchase #4	$56.82	11.357%	$63.273	$63.27	$63.25	$63.30
Purchase #5	$68.72	6.652%	$73.2913	$73.29	$73.30	$73.30
Purchase #6	$220.27	5.470%	$232.3188	$232.32	$232.30	$232.30
Purchase #7	$114.40	8.117%	$123.6858	$123.69	$123.70	$123.70
7 purchase totals =	$729.07		$789.3990	$789.40	$789.35	$789.50