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	$46.52	9.583%	$50.978	$50.98	$51.00	$51.00
Purchase #2	$139.38	6.104%	$147.8878	$147.89	$147.90	$147.90
Purchase #3	$147.49	12.307%	$165.6416	$165.64	$165.65	$165.60
Purchase #4	$123.35	13.791%	$140.3612	$140.36	$140.35	$140.40
Purchase #5	$108.27	10.666%	$119.8181	$119.82	$119.80	$119.80
Purchase #6	$185.68	12.163%	$208.2643	$208.26	$208.25	$208.30
Purchase #7	$239.49	13.607%	$272.0774	$272.08	$272.10	$272.10
7 purchase totals =	$990.18		$1,105.0284	$1,105.03	$1,105.05	$1,105.10