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	$28.55	11.279%	$31.7702	$31.77	$31.75	$31.80
Purchase #2	$139.98	9.608%	$153.4293	$153.43	$153.45	$153.40
Purchase #3	$83.79	8.358%	$90.7932	$90.79	$90.80	$90.80
Purchase #4	$47.80	13.823%	$54.4074	$54.41	$54.40	$54.40
Purchase #5	$165.45	3.729%	$171.6196	$171.62	$171.60	$171.60
Purchase #6	$224.27	3.214%	$231.478	$231.48	$231.50	$231.50
Purchase #7	$214.60	10.746%	$237.6609	$237.66	$237.65	$237.70
7 purchase totals =	$904.44		$971.1586	$971.16	$971.15	$971.20