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	$243.81	11.280%	$271.3118	$271.31	$271.30	$271.30
Purchase #2	$87.90	13.160%	$99.4676	$99.47	$99.45	$99.50
Purchase #3	$140.28	13.769%	$159.5952	$159.60	$159.60	$159.60
Purchase #4	$65.28	7.573%	$70.2237	$70.22	$70.20	$70.20
Purchase #5	$75.52	3.674%	$78.2946	$78.29	$78.30	$78.30
Purchase #6	$46.31	10.847%	$51.3332	$51.33	$51.35	$51.30
Purchase #7	$24.58	11.487%	$27.4035	$27.40	$27.40	$27.40
7 purchase totals =	$683.68		$757.6296	$757.62	$757.60	$757.60