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	$85.60	6.404%	$91.0818	$91.08	$91.10	$91.10
Purchase #2	$170.70	8.320%	$184.9022	$184.90	$184.90	$184.90
Purchase #3	$170.61	5.509%	$180.0089	$180.01	$180.00	$180.00
Purchase #4	$43.35	9.584%	$47.5047	$47.50	$47.50	$47.50
Purchase #5	$244.69	11.447%	$272.6997	$272.70	$272.70	$272.70
Purchase #6	$37.71	11.731%	$42.1338	$42.13	$42.15	$42.10
Purchase #7	$169.67	12.243%	$190.4427	$190.44	$190.45	$190.40
7 purchase totals =	$922.33		$1,008.7738	$1,008.76	$1,008.80	$1,008.70