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	$162.39	3.169%	$167.5361	$167.54	$167.55	$167.50
Purchase #2	$47.85	7.844%	$51.6034	$51.60	$51.60	$51.60
Purchase #3	$91.72	12.574%	$103.2529	$103.25	$103.25	$103.30
Purchase #4	$236.49	12.382%	$265.7722	$265.77	$265.75	$265.80
Purchase #5	$23.70	11.454%	$26.4146	$26.41	$26.40	$26.40
Purchase #6	$115.59	13.739%	$131.4709	$131.47	$131.45	$131.50
Purchase #7	$129.80	10.393%	$143.2901	$143.29	$143.30	$143.30
7 purchase totals =	$807.54		$889.3402	$889.33	$889.30	$889.40