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	$18.86	3.134%	$19.4511	$19.45	$19.45	$19.50
Purchase #2	$223.33	7.263%	$239.5505	$239.55	$239.55	$239.60
Purchase #3	$78.72	13.381%	$89.2535	$89.25	$89.25	$89.30
Purchase #4	$216.92	6.849%	$231.7769	$231.78	$231.80	$231.80
Purchase #5	$6.39	3.175%	$6.5929	$6.59	$6.60	$6.60
Purchase #6	$118.78	11.594%	$132.5514	$132.55	$132.55	$132.60
Purchase #7	$48.30	9.362%	$52.8218	$52.82	$52.80	$52.80
7 purchase totals =	$711.30		$771.9981	$771.99	$772.00	$772.20