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	$127.32	13.678%	$144.7348	$144.73	$144.75	$144.70
Purchase #2	$38.33	11.738%	$42.8292	$42.83	$42.85	$42.80
Purchase #3	$30.98	9.699%	$33.9848	$33.98	$34.00	$34.00
Purchase #4	$83.46	10.692%	$92.3835	$92.38	$92.40	$92.40
Purchase #5	$212.89	11.547%	$237.4724	$237.47	$237.45	$237.50
Purchase #6	$144.69	8.305%	$156.7065	$156.71	$156.70	$156.70
Purchase #7	$102.69	4.749%	$107.5667	$107.57	$107.55	$107.60
7 purchase totals =	$740.36		$815.6779	$815.67	$815.70	$815.70