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	$65.90	9.112%	$71.9048	$71.90	$71.90	$71.90
Purchase #2	$126.49	3.863%	$131.3763	$131.38	$131.40	$131.40
Purchase #3	$227.25	6.190%	$241.3168	$241.32	$241.30	$241.30
Purchase #4	$101.35	10.643%	$112.1367	$112.14	$112.15	$112.10
Purchase #5	$5.72	9.598%	$6.269	$6.27	$6.25	$6.30
Purchase #6	$121.34	12.267%	$136.2248	$136.22	$136.20	$136.20
Purchase #7	$98.75	13.324%	$111.9075	$111.91	$111.90	$111.90
7 purchase totals =	$746.80		$811.1359	$811.14	$811.10	$811.10