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	$221.95	9.521%	$243.0819	$243.08	$243.10	$243.10
Purchase #2	$96.47	8.788%	$104.9478	$104.95	$104.95	$104.90
Purchase #3	$82.71	12.178%	$92.7824	$92.78	$92.80	$92.80
Purchase #4	$7.42	13.555%	$8.4258	$8.43	$8.45	$8.40
Purchase #5	$67.32	6.810%	$71.9045	$71.90	$71.90	$71.90
Purchase #6	$111.62	7.280%	$119.7459	$119.75	$119.75	$119.70
Purchase #7	$21.52	13.238%	$24.3688	$24.37	$24.35	$24.40
7 purchase totals =	$609.01		$665.2571	$665.26	$665.30	$665.20