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	$240.80	4.695%	$252.1056	$252.11	$252.10	$252.10
Purchase #2	$40.77	8.587%	$44.2709	$44.27	$44.25	$44.30
Purchase #3	$60.36	6.663%	$64.3818	$64.38	$64.40	$64.40
Purchase #4	$107.31	4.287%	$111.9104	$111.91	$111.90	$111.90
Purchase #5	$249.87	5.811%	$264.3899	$264.39	$264.40	$264.40
Purchase #6	$217.59	9.499%	$238.2589	$238.26	$238.25	$238.30
Purchase #7	$32.72	13.535%	$37.1487	$37.15	$37.15	$37.10
7 purchase totals =	$949.42		$1,012.4662	$1,012.47	$1,012.45	$1,012.50