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	$42.72	8.605%	$46.3961	$46.40	$46.40	$46.40
Purchase #2	$100.36	7.187%	$107.5729	$107.57	$107.55	$107.60
Purchase #3	$134.54	13.333%	$152.4782	$152.48	$152.50	$152.50
Purchase #4	$158.93	6.287%	$168.9219	$168.92	$168.90	$168.90
Purchase #5	$95.35	9.248%	$104.168	$104.17	$104.15	$104.20
Purchase #6	$30.71	3.297%	$31.7225	$31.72	$31.70	$31.70
Purchase #7	$121.83	5.652%	$128.7158	$128.72	$128.70	$128.70
7 purchase totals =	$684.44		$739.9754	$739.98	$739.90	$740.00