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	$122.64	6.678%	$130.8299	$130.83	$130.85	$130.80
Purchase #2	$195.62	4.524%	$204.4698	$204.47	$204.45	$204.50
Purchase #3	$210.78	9.355%	$230.4985	$230.50	$230.50	$230.50
Purchase #4	$103.34	5.489%	$109.0123	$109.01	$109.00	$109.00
Purchase #5	$230.60	8.794%	$250.879	$250.88	$250.90	$250.90
Purchase #6	$92.76	12.334%	$104.201	$104.20	$104.20	$104.20
Purchase #7	$132.69	13.568%	$150.6934	$150.69	$150.70	$150.70
7 purchase totals =	$1,088.43		$1,180.5839	$1,180.58	$1,180.60	$1,180.60