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	$80.33	12.234%	$90.1576	$90.16	$90.15	$90.20
Purchase #2	$113.52	5.674%	$119.9611	$119.96	$119.95	$120.00
Purchase #3	$88.96	11.166%	$98.8933	$98.89	$98.90	$98.90
Purchase #4	$225.60	12.848%	$254.5851	$254.59	$254.60	$254.60
Purchase #5	$210.96	3.772%	$218.9174	$218.92	$218.90	$218.90
Purchase #6	$83.84	6.126%	$88.976	$88.98	$89.00	$89.00
Purchase #7	$34.80	12.331%	$39.0912	$39.09	$39.10	$39.10
7 purchase totals =	$838.01		$910.5817	$910.59	$910.60	$910.70