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	$228.42	8.444%	$247.7078	$247.71	$247.70	$247.70
Purchase #2	$102.45	8.504%	$111.1623	$111.16	$111.15	$111.20
Purchase #3	$88.53	11.380%	$98.6047	$98.60	$98.60	$98.60
Purchase #4	$175.70	13.437%	$199.3088	$199.31	$199.30	$199.30
Purchase #5	$244.86	5.693%	$258.7999	$258.80	$258.80	$258.80
Purchase #6	$111.97	13.566%	$127.1599	$127.16	$127.15	$127.20
Purchase #7	$224.46	9.270%	$245.2674	$245.27	$245.25	$245.30
7 purchase totals =	$1,176.39		$1,288.0108	$1,288.01	$1,287.95	$1,288.10