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	$157.40	11.190%	$175.0131	$175.01	$175.00	$175.00
Purchase #2	$49.74	13.527%	$56.4683	$56.47	$56.45	$56.50
Purchase #3	$232.31	11.273%	$258.4983	$258.50	$258.50	$258.50
Purchase #4	$29.29	13.240%	$33.168	$33.17	$33.15	$33.20
Purchase #5	$82.55	8.757%	$89.7789	$89.78	$89.80	$89.80
Purchase #6	$117.30	8.349%	$127.0934	$127.09	$127.10	$127.10
Purchase #7	$177.96	12.225%	$199.7156	$199.72	$199.70	$199.70
7 purchase totals =	$846.55		$939.7356	$939.74	$939.70	$939.80