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	$236.74	5.409%	$249.5453	$249.55	$249.55	$249.50
Purchase #2	$196.81	13.115%	$222.6216	$222.62	$222.60	$222.60
Purchase #3	$67.42	13.344%	$76.4165	$76.42	$76.40	$76.40
Purchase #4	$134.49	3.776%	$139.5683	$139.57	$139.55	$139.60
Purchase #5	$68.27	3.443%	$70.6205	$70.62	$70.60	$70.60
Purchase #6	$57.81	3.237%	$59.6813	$59.68	$59.70	$59.70
Purchase #7	$41.34	5.498%	$43.6129	$43.61	$43.60	$43.60
7 purchase totals =	$802.88		$862.0664	$862.07	$862.00	$862.00