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	$192.96	10.171%	$212.586	$212.59	$212.60	$212.60
Purchase #2	$136.46	10.834%	$151.2441	$151.24	$151.25	$151.20
Purchase #3	$16.99	7.766%	$18.3094	$18.31	$18.30	$18.30
Purchase #4	$151.41	11.358%	$168.6071	$168.61	$168.60	$168.60
Purchase #5	$229.29	6.320%	$243.7811	$243.78	$243.80	$243.80
Purchase #6	$48.30	7.674%	$52.0065	$52.01	$52.00	$52.00
Purchase #7	$12.75	3.388%	$13.182	$13.18	$13.20	$13.20
7 purchase totals =	$788.16		$859.7162	$859.72	$859.75	$859.70