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	$34.79	10.334%	$38.3852	$38.39	$38.40	$38.40
Purchase #2	$65.55	6.494%	$69.8068	$69.81	$69.80	$69.80
Purchase #3	$92.82	8.412%	$100.628	$100.63	$100.65	$100.60
Purchase #4	$212.85	9.813%	$233.737	$233.74	$233.75	$233.70
Purchase #5	$100.92	10.508%	$111.5247	$111.52	$111.50	$111.50
Purchase #6	$59.50	8.105%	$64.3225	$64.32	$64.30	$64.30
Purchase #7	$169.35	9.826%	$185.9903	$185.99	$186.00	$186.00
7 purchase totals =	$735.78		$804.3945	$804.40	$804.40	$804.30