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	$47.71	7.827%	$51.4443	$51.44	$51.45	$51.40
Purchase #2	$25.66	7.594%	$27.6086	$27.61	$27.60	$27.60
Purchase #3	$89.99	12.802%	$101.5105	$101.51	$101.50	$101.50
Purchase #4	$122.45	7.401%	$131.5125	$131.51	$131.50	$131.50
Purchase #5	$41.33	3.280%	$42.6856	$42.69	$42.70	$42.70
Purchase #6	$211.30	8.680%	$229.6408	$229.64	$229.65	$229.60
Purchase #7	$209.58	5.221%	$220.5222	$220.52	$220.50	$220.50
7 purchase totals =	$748.02		$804.9245	$804.92	$804.90	$804.80