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	$7.86	9.394%	$8.5984	$8.60	$8.60	$8.60
Purchase #2	$19.42	8.673%	$21.1043	$21.10	$21.10	$21.10
Purchase #3	$90.93	12.737%	$102.5118	$102.51	$102.50	$102.50
Purchase #4	$64.84	9.812%	$71.2021	$71.20	$71.20	$71.20
Purchase #5	$245.41	7.836%	$264.6403	$264.64	$264.65	$264.60
Purchase #6	$180.45	8.837%	$196.3964	$196.40	$196.40	$196.40
Purchase #7	$48.37	4.248%	$50.4248	$50.42	$50.40	$50.40
7 purchase totals =	$657.28		$714.8781	$714.87	$714.85	$714.80