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	$59.81	10.661%	$66.1863	$66.19	$66.20	$66.20
Purchase #2	$63.54	5.804%	$67.2279	$67.23	$67.25	$67.20
Purchase #3	$158.71	9.779%	$174.2303	$174.23	$174.25	$174.20
Purchase #4	$14.45	9.533%	$15.8275	$15.83	$15.85	$15.80
Purchase #5	$103.88	7.389%	$111.5557	$111.56	$111.55	$111.60
Purchase #6	$120.47	12.632%	$135.6878	$135.69	$135.70	$135.70
Purchase #7	$125.30	3.831%	$130.1002	$130.10	$130.10	$130.10
7 purchase totals =	$646.16		$700.8157	$700.83	$700.90	$700.80