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	$40.26	5.739%	$42.5705	$42.57	$42.55	$42.60
Purchase #2	$103.78	11.700%	$115.9223	$115.92	$115.90	$115.90
Purchase #3	$184.32	6.264%	$195.8658	$195.87	$195.85	$195.90
Purchase #4	$108.52	8.744%	$118.009	$118.01	$118.00	$118.00
Purchase #5	$173.61	7.780%	$187.1169	$187.12	$187.10	$187.10
Purchase #6	$50.81	13.766%	$57.8045	$57.80	$57.80	$57.80
Purchase #7	$81.48	10.735%	$90.2269	$90.23	$90.25	$90.20
7 purchase totals =	$742.78		$807.5159	$807.52	$807.45	$807.50