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	$205.47	6.769%	$219.3783	$219.38	$219.40	$219.40
Purchase #2	$65.70	9.722%	$72.0874	$72.09	$72.10	$72.10
Purchase #3	$57.78	10.462%	$63.8249	$63.82	$63.80	$63.80
Purchase #4	$186.84	4.163%	$194.6181	$194.62	$194.60	$194.60
Purchase #5	$74.95	7.359%	$80.4656	$80.47	$80.45	$80.50
Purchase #6	$169.78	3.398%	$175.5491	$175.55	$175.55	$175.50
Purchase #7	$242.52	13.549%	$275.379	$275.38	$275.40	$275.40
7 purchase totals =	$1,003.04		$1,081.3024	$1,081.31	$1,081.30	$1,081.30