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	$137.89	6.386%	$146.6957	$146.70	$146.70	$146.70
Purchase #2	$127.35	13.545%	$144.5996	$144.60	$144.60	$144.60
Purchase #3	$165.69	5.789%	$175.2818	$175.28	$175.30	$175.30
Purchase #4	$94.77	12.314%	$106.44	$106.44	$106.45	$106.40
Purchase #5	$243.29	5.151%	$255.8219	$255.82	$255.80	$255.80
Purchase #6	$46.37	13.342%	$52.5567	$52.56	$52.55	$52.60
Purchase #7	$220.96	12.858%	$249.371	$249.37	$249.35	$249.40
7 purchase totals =	$1,036.32		$1,130.7667	$1,130.77	$1,130.75	$1,130.80