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	$93.41	6.441%	$99.4265	$99.43	$99.45	$99.40
Purchase #2	$48.68	3.779%	$50.5196	$50.52	$50.50	$50.50
Purchase #3	$18.82	10.296%	$20.7577	$20.76	$20.75	$20.80
Purchase #4	$227.67	5.856%	$241.0024	$241.00	$241.00	$241.00
Purchase #5	$42.94	8.542%	$46.6079	$46.61	$46.60	$46.60
Purchase #6	$50.71	8.861%	$55.2034	$55.20	$55.20	$55.20
Purchase #7	$19.66	8.805%	$21.3911	$21.39	$21.40	$21.40
7 purchase totals =	$501.89		$534.9086	$534.91	$534.90	$534.90