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	$249.59	11.565%	$278.4551	$278.46	$278.45	$278.50
Purchase #2	$34.89	6.529%	$37.168	$37.17	$37.15	$37.20
Purchase #3	$10.73	5.532%	$11.3236	$11.32	$11.30	$11.30
Purchase #4	$38.42	3.563%	$39.7889	$39.79	$39.80	$39.80
Purchase #5	$95.84	5.222%	$100.8448	$100.84	$100.85	$100.80
Purchase #6	$8.56	7.747%	$9.2231	$9.22	$9.20	$9.20
Purchase #7	$50.58	3.659%	$52.4307	$52.43	$52.45	$52.40
7 purchase totals =	$488.61		$529.2342	$529.23	$529.20	$529.20