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	$28.77	10.161%	$31.6933	$31.69	$31.70	$31.70
Purchase #2	$71.61	9.197%	$78.196	$78.20	$78.20	$78.20
Purchase #3	$144.82	4.519%	$151.3644	$151.36	$151.35	$151.40
Purchase #4	$85.62	5.599%	$90.4139	$90.41	$90.40	$90.40
Purchase #5	$18.77	13.667%	$21.3353	$21.34	$21.35	$21.30
Purchase #6	$33.68	12.538%	$37.9028	$37.90	$37.90	$37.90
Purchase #7	$46.28	5.343%	$48.7527	$48.75	$48.75	$48.80
7 purchase totals =	$429.55		$459.6584	$459.65	$459.65	$459.70