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	$103.40	13.437%	$117.2939	$117.29	$117.30	$117.30
Purchase #2	$55.40	7.635%	$59.6298	$59.63	$59.65	$59.60
Purchase #3	$66.37	11.642%	$74.0968	$74.10	$74.10	$74.10
Purchase #4	$210.41	9.558%	$230.521	$230.52	$230.50	$230.50
Purchase #5	$200.46	7.272%	$215.0375	$215.04	$215.05	$215.00
Purchase #6	$212.36	11.496%	$236.7729	$236.77	$236.75	$236.80
Purchase #7	$42.82	5.459%	$45.1575	$45.16	$45.15	$45.20
7 purchase totals =	$891.22		$978.5094	$978.51	$978.50	$978.50