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	$229.46	7.462%	$246.5823	$246.58	$246.60	$246.60
Purchase #2	$105.33	12.477%	$118.472	$118.47	$118.45	$118.50
Purchase #3	$245.34	8.538%	$266.2871	$266.29	$266.30	$266.30
Purchase #4	$61.98	3.396%	$64.0848	$64.08	$64.10	$64.10
Purchase #5	$64.42	13.732%	$73.2662	$73.27	$73.25	$73.30
Purchase #6	$28.40	13.711%	$32.2939	$32.29	$32.30	$32.30
Purchase #7	$29.27	10.598%	$32.372	$32.37	$32.35	$32.40
7 purchase totals =	$764.20		$833.3583	$833.35	$833.35	$833.50