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	$57.36	11.418%	$63.9094	$63.91	$63.90	$63.90
Purchase #2	$89.95	11.777%	$100.5434	$100.54	$100.55	$100.50
Purchase #3	$180.73	13.168%	$204.5285	$204.53	$204.55	$204.50
Purchase #4	$53.57	6.635%	$57.1244	$57.12	$57.10	$57.10
Purchase #5	$63.74	10.415%	$70.3785	$70.38	$70.40	$70.40
Purchase #6	$98.71	8.314%	$106.9167	$106.92	$106.90	$106.90
Purchase #7	$56.52	5.174%	$59.4443	$59.44	$59.45	$59.40
7 purchase totals =	$600.58		$662.8452	$662.84	$662.85	$662.70