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	$139.40	3.827%	$144.7348	$144.73	$144.75	$144.70
Purchase #2	$160.89	12.797%	$181.4791	$181.48	$181.50	$181.50
Purchase #3	$64.68	6.852%	$69.1119	$69.11	$69.10	$69.10
Purchase #4	$171.73	4.510%	$179.475	$179.48	$179.50	$179.50
Purchase #5	$66.60	10.667%	$73.7042	$73.70	$73.70	$73.70
Purchase #6	$87.48	4.192%	$91.1472	$91.15	$91.15	$91.10
Purchase #7	$96.94	13.335%	$109.8669	$109.87	$109.85	$109.90
7 purchase totals =	$787.72		$849.5191	$849.52	$849.55	$849.50