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	$235.87	6.629%	$251.5058	$251.51	$251.50	$251.50
Purchase #2	$161.47	3.794%	$167.5962	$167.60	$167.60	$167.60
Purchase #3	$84.25	12.531%	$94.8074	$94.81	$94.80	$94.80
Purchase #4	$182.60	7.675%	$196.6146	$196.61	$196.60	$196.60
Purchase #5	$121.90	9.361%	$133.3111	$133.31	$133.30	$133.30
Purchase #6	$99.46	5.409%	$104.8398	$104.84	$104.85	$104.80
Purchase #7	$10.75	11.694%	$12.0071	$12.01	$12.00	$12.00
7 purchase totals =	$896.30		$960.6820	$960.69	$960.65	$960.60