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	$144.73	10.460%	$159.8688	$159.87	$159.85	$159.90
Purchase #2	$191.63	4.830%	$200.8857	$200.89	$200.90	$200.90
Purchase #3	$229.86	5.525%	$242.5598	$242.56	$242.55	$242.60
Purchase #4	$150.34	13.490%	$170.6209	$170.62	$170.60	$170.60
Purchase #5	$176.92	8.277%	$191.5637	$191.56	$191.55	$191.60
Purchase #6	$44.56	7.329%	$47.8258	$47.83	$47.85	$47.80
Purchase #7	$197.97	13.751%	$225.1929	$225.19	$225.20	$225.20
7 purchase totals =	$1,136.01		$1,238.5176	$1,238.52	$1,238.50	$1,238.60