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	$38.26	11.771%	$42.7636	$42.76	$42.75	$42.80
Purchase #2	$60.67	11.661%	$67.7447	$67.74	$67.75	$67.70
Purchase #3	$131.86	8.513%	$143.0852	$143.09	$143.10	$143.10
Purchase #4	$41.35	7.581%	$44.4847	$44.48	$44.50	$44.50
Purchase #5	$226.33	4.654%	$236.8634	$236.86	$236.85	$236.90
Purchase #6	$92.76	8.452%	$100.6001	$100.60	$100.60	$100.60
Purchase #7	$102.64	4.495%	$107.2537	$107.25	$107.25	$107.30
7 purchase totals =	$693.87		$742.7954	$742.78	$742.80	$742.90