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	$127.33	9.785%	$139.7892	$139.79	$139.80	$139.80
Purchase #2	$119.89	8.765%	$130.3984	$130.40	$130.40	$130.40
Purchase #3	$49.52	8.621%	$53.7891	$53.79	$53.80	$53.80
Purchase #4	$208.51	3.685%	$216.1936	$216.19	$216.20	$216.20
Purchase #5	$204.51	7.484%	$219.8155	$219.82	$219.80	$219.80
Purchase #6	$86.39	5.169%	$90.8555	$90.86	$90.85	$90.90
Purchase #7	$71.89	9.821%	$78.9503	$78.95	$78.95	$79.00
7 purchase totals =	$868.04		$929.7916	$929.80	$929.80	$929.90