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	$159.92	6.218%	$169.8638	$169.86	$169.85	$169.90
Purchase #2	$39.95	5.514%	$42.1528	$42.15	$42.15	$42.20
Purchase #3	$106.91	8.646%	$116.1534	$116.15	$116.15	$116.20
Purchase #4	$221.61	6.806%	$236.6928	$236.69	$236.70	$236.70
Purchase #5	$49.27	9.865%	$54.1305	$54.13	$54.15	$54.10
Purchase #6	$228.86	13.557%	$259.8866	$259.89	$259.90	$259.90
Purchase #7	$46.28	3.467%	$47.8845	$47.88	$47.90	$47.90
7 purchase totals =	$852.80		$926.7644	$926.75	$926.80	$926.90