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	$151.28	13.232%	$171.2974	$171.30	$171.30	$171.30
Purchase #2	$89.91	6.229%	$95.5105	$95.51	$95.50	$95.50
Purchase #3	$47.41	7.840%	$51.1269	$51.13	$51.15	$51.10
Purchase #4	$141.47	13.526%	$160.6052	$160.61	$160.60	$160.60
Purchase #5	$120.66	7.298%	$129.4658	$129.47	$129.45	$129.50
Purchase #6	$166.45	3.112%	$171.6299	$171.63	$171.65	$171.60
Purchase #7	$45.59	8.149%	$49.3051	$49.31	$49.30	$49.30
7 purchase totals =	$762.77		$828.9408	$828.96	$828.95	$828.90