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	$44.89	12.690%	$50.5865	$50.59	$50.60	$50.60
Purchase #2	$185.29	7.288%	$198.7939	$198.79	$198.80	$198.80
Purchase #3	$131.44	7.755%	$141.6332	$141.63	$141.65	$141.60
Purchase #4	$78.59	9.461%	$86.0254	$86.03	$86.05	$86.00
Purchase #5	$146.52	12.822%	$165.3068	$165.31	$165.30	$165.30
Purchase #6	$52.45	10.639%	$58.0302	$58.03	$58.05	$58.00
Purchase #7	$11.71	3.263%	$12.0921	$12.09	$12.10	$12.10
7 purchase totals =	$650.89		$712.4681	$712.47	$712.55	$712.40