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	$138.74	3.623%	$143.7666	$143.77	$143.75	$143.80
Purchase #2	$103.26	9.222%	$112.7826	$112.78	$112.80	$112.80
Purchase #3	$141.62	13.593%	$160.8704	$160.87	$160.85	$160.90
Purchase #4	$27.39	8.413%	$29.6943	$29.69	$29.70	$29.70
Purchase #5	$112.42	9.427%	$123.0178	$123.02	$123.00	$123.00
Purchase #6	$85.95	11.570%	$95.8944	$95.89	$95.90	$95.90
Purchase #7	$28.51	6.745%	$30.433	$30.43	$30.45	$30.40
7 purchase totals =	$637.89		$696.4591	$696.45	$696.45	$696.50