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	$215.90	3.702%	$223.8926	$223.89	$223.90	$223.90
Purchase #2	$192.96	11.678%	$215.4939	$215.49	$215.50	$215.50
Purchase #3	$130.80	11.498%	$145.8394	$145.84	$145.85	$145.80
Purchase #4	$130.72	6.724%	$139.5096	$139.51	$139.50	$139.50
Purchase #5	$228.66	9.318%	$249.9665	$249.97	$249.95	$250.00
Purchase #6	$45.86	13.148%	$51.8897	$51.89	$51.90	$51.90
Purchase #7	$119.60	4.323%	$124.7703	$124.77	$124.75	$124.80
7 purchase totals =	$1,064.50		$1,151.3620	$1,151.36	$1,151.35	$1,151.40