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	$78.87	6.807%	$84.2387	$84.24	$84.25	$84.20
Purchase #2	$163.89	11.743%	$183.1356	$183.14	$183.15	$183.10
Purchase #3	$189.82	3.484%	$196.4333	$196.43	$196.45	$196.40
Purchase #4	$47.90	6.506%	$51.0164	$51.02	$51.00	$51.00
Purchase #5	$244.91	4.392%	$255.6664	$255.67	$255.65	$255.70
Purchase #6	$111.95	5.310%	$117.8945	$117.89	$117.90	$117.90
Purchase #7	$85.26	6.262%	$90.599	$90.60	$90.60	$90.60
7 purchase totals =	$922.60		$978.9839	$978.99	$979.00	$978.90