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	$42.37	4.623%	$44.3288	$44.33	$44.35	$44.30
Purchase #2	$146.47	12.121%	$164.2236	$164.22	$164.20	$164.20
Purchase #3	$42.30	13.147%	$47.8612	$47.86	$47.85	$47.90
Purchase #4	$29.81	12.711%	$33.5991	$33.60	$33.60	$33.60
Purchase #5	$139.60	4.865%	$146.3915	$146.39	$146.40	$146.40
Purchase #6	$177.64	12.315%	$199.5164	$199.52	$199.50	$199.50
Purchase #7	$52.64	5.201%	$55.3778	$55.38	$55.40	$55.40
7 purchase totals =	$630.83		$691.2984	$691.30	$691.30	$691.30