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	$35.86	13.597%	$40.7359	$40.74	$40.75	$40.70
Purchase #2	$126.30	12.145%	$141.6391	$141.64	$141.65	$141.60
Purchase #3	$222.81	9.293%	$243.5157	$243.52	$243.50	$243.50
Purchase #4	$64.30	12.579%	$72.3883	$72.39	$72.40	$72.40
Purchase #5	$61.72	9.784%	$67.7587	$67.76	$67.75	$67.80
Purchase #6	$73.68	4.273%	$76.8283	$76.83	$76.85	$76.80
Purchase #7	$157.38	4.676%	$164.7391	$164.74	$164.75	$164.70
7 purchase totals =	$742.05		$807.6051	$807.62	$807.65	$807.50