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	$105.45	13.482%	$119.6668	$119.67	$119.65	$119.70
Purchase #2	$230.48	12.469%	$259.2186	$259.22	$259.20	$259.20
Purchase #3	$153.25	7.673%	$165.0089	$165.01	$165.00	$165.00
Purchase #4	$67.75	4.538%	$70.8245	$70.82	$70.80	$70.80
Purchase #5	$51.85	11.623%	$57.8765	$57.88	$57.90	$57.90
Purchase #6	$51.90	3.784%	$53.8639	$53.86	$53.85	$53.90
Purchase #7	$120.48	9.261%	$131.6377	$131.64	$131.65	$131.60
7 purchase totals =	$781.16		$858.0969	$858.10	$858.05	$858.10