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	$232.28	5.698%	$245.5153	$245.52	$245.50	$245.50
Purchase #2	$110.67	11.628%	$123.5387	$123.54	$123.55	$123.50
Purchase #3	$22.61	4.643%	$23.6598	$23.66	$23.65	$23.70
Purchase #4	$52.87	8.713%	$57.4766	$57.48	$57.50	$57.50
Purchase #5	$10.41	10.201%	$11.4719	$11.47	$11.45	$11.50
Purchase #6	$189.82	3.356%	$196.1904	$196.19	$196.20	$196.20
Purchase #7	$164.66	12.577%	$185.3693	$185.37	$185.35	$185.40
7 purchase totals =	$783.32		$843.2220	$843.23	$843.20	$843.30