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	$225.83	10.708%	$250.0119	$250.01	$250.00	$250.00
Purchase #2	$146.72	10.684%	$162.3956	$162.40	$162.40	$162.40
Purchase #3	$67.82	5.436%	$71.5067	$71.51	$71.50	$71.50
Purchase #4	$62.26	13.526%	$70.6813	$70.68	$70.70	$70.70
Purchase #5	$238.25	4.656%	$249.3429	$249.34	$249.35	$249.30
Purchase #6	$94.87	10.546%	$104.875	$104.88	$104.90	$104.90
Purchase #7	$107.49	3.822%	$111.5983	$111.60	$111.60	$111.60
7 purchase totals =	$943.24		$1,020.4117	$1,020.42	$1,020.45	$1,020.40