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	$126.86	13.368%	$143.8186	$143.82	$143.80	$143.80
Purchase #2	$143.52	7.644%	$154.4907	$154.49	$154.50	$154.50
Purchase #3	$46.79	5.578%	$49.3999	$49.40	$49.40	$49.40
Purchase #4	$78.27	7.789%	$84.3665	$84.37	$84.35	$84.40
Purchase #5	$67.55	6.455%	$71.9104	$71.91	$71.90	$71.90
Purchase #6	$227.87	7.694%	$245.4023	$245.40	$245.40	$245.40
Purchase #7	$133.88	13.138%	$151.4692	$151.47	$151.45	$151.50
7 purchase totals =	$824.74		$900.8576	$900.86	$900.80	$900.90