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	$71.52	4.150%	$74.4881	$74.49	$74.50	$74.50
Purchase #2	$82.60	3.427%	$85.4307	$85.43	$85.45	$85.40
Purchase #3	$248.56	7.161%	$266.3594	$266.36	$266.35	$266.40
Purchase #4	$244.66	12.703%	$275.7392	$275.74	$275.75	$275.70
Purchase #5	$122.88	13.391%	$139.3349	$139.33	$139.35	$139.30
Purchase #6	$60.83	7.800%	$65.5747	$65.57	$65.55	$65.60
Purchase #7	$134.83	5.736%	$142.5638	$142.56	$142.55	$142.60
7 purchase totals =	$965.88		$1,049.4908	$1,049.48	$1,049.50	$1,049.50