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	$10.31	3.233%	$10.6433	$10.64	$10.65	$10.60
Purchase #2	$224.81	6.281%	$238.9303	$238.93	$238.95	$238.90
Purchase #3	$234.55	10.670%	$259.5765	$259.58	$259.60	$259.60
Purchase #4	$18.49	7.583%	$19.8921	$19.89	$19.90	$19.90
Purchase #5	$6.55	6.773%	$6.9936	$6.99	$7.00	$7.00
Purchase #6	$157.43	3.826%	$163.4533	$163.45	$163.45	$163.50
Purchase #7	$185.41	6.192%	$196.8906	$196.89	$196.90	$196.90
7 purchase totals =	$837.55		$896.3797	$896.37	$896.45	$896.40