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	$109.72	12.493%	$123.4273	$123.43	$123.45	$123.40
Purchase #2	$112.51	5.834%	$119.0738	$119.07	$119.05	$119.10
Purchase #3	$29.46	11.280%	$32.7831	$32.78	$32.80	$32.80
Purchase #4	$154.79	9.128%	$168.9192	$168.92	$168.90	$168.90
Purchase #5	$98.36	7.309%	$105.5491	$105.55	$105.55	$105.50
Purchase #6	$32.42	12.209%	$36.3782	$36.38	$36.40	$36.40
Purchase #7	$200.74	8.127%	$217.0541	$217.05	$217.05	$217.10
7 purchase totals =	$738.00		$803.1848	$803.18	$803.20	$803.20