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	$95.60	5.470%	$100.8293	$100.83	$100.85	$100.80
Purchase #2	$148.80	6.300%	$158.1744	$158.17	$158.15	$158.20
Purchase #3	$82.39	9.780%	$90.4477	$90.45	$90.45	$90.40
Purchase #4	$239.68	13.220%	$271.3657	$271.37	$271.35	$271.40
Purchase #5	$80.78	10.140%	$88.9711	$88.97	$88.95	$89.00
Purchase #6	$234.32	5.360%	$246.8796	$246.88	$246.90	$246.90
Purchase #7	$155.31	6.671%	$165.6707	$165.67	$165.65	$165.70
7 purchase totals =	$1,036.88		$1,122.3385	$1,122.34	$1,122.30	$1,122.40