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	$134.28	5.611%	$141.8145	$141.81	$141.80	$141.80
Purchase #2	$149.52	10.861%	$165.7594	$165.76	$165.75	$165.80
Purchase #3	$188.69	8.857%	$205.4023	$205.40	$205.40	$205.40
Purchase #4	$116.33	10.475%	$128.5156	$128.52	$128.50	$128.50
Purchase #5	$36.38	12.470%	$40.9166	$40.92	$40.90	$40.90
Purchase #6	$205.98	13.300%	$233.3753	$233.38	$233.40	$233.40
Purchase #7	$200.75	5.779%	$212.3513	$212.35	$212.35	$212.40
7 purchase totals =	$1,031.93		$1,128.1350	$1,128.14	$1,128.10	$1,128.20