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	$21.77	7.500%	$23.4028	$23.40	$23.40	$23.40
Purchase #2	$126.85	12.604%	$142.8382	$142.84	$142.85	$142.80
Purchase #3	$104.80	6.789%	$111.9149	$111.91	$111.90	$111.90
Purchase #4	$148.65	13.439%	$168.6271	$168.63	$168.65	$168.60
Purchase #5	$43.47	5.794%	$45.9887	$45.99	$46.00	$46.00
Purchase #6	$229.59	3.823%	$238.3672	$238.37	$238.35	$238.40
Purchase #7	$106.57	7.714%	$114.7908	$114.79	$114.80	$114.80
7 purchase totals =	$781.70		$845.9297	$845.93	$845.95	$845.90