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	$103.37	10.842%	$114.5774	$114.58	$114.60	$114.60
Purchase #2	$37.57	13.793%	$42.752	$42.75	$42.75	$42.80
Purchase #3	$36.60	13.348%	$41.4854	$41.49	$41.50	$41.50
Purchase #4	$174.38	7.377%	$187.244	$187.24	$187.25	$187.20
Purchase #5	$249.85	11.847%	$279.4497	$279.45	$279.45	$279.40
Purchase #6	$98.61	6.104%	$104.6292	$104.63	$104.65	$104.60
Purchase #7	$55.51	6.397%	$59.061	$59.06	$59.05	$59.10
7 purchase totals =	$755.89		$829.1987	$829.20	$829.25	$829.20