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	$66.47	7.736%	$71.6121	$71.61	$71.60	$71.60
Purchase #2	$179.68	4.377%	$187.5446	$187.54	$187.55	$187.50
Purchase #3	$137.51	9.789%	$150.9709	$150.97	$150.95	$151.00
Purchase #4	$95.36	13.694%	$108.4186	$108.42	$108.40	$108.40
Purchase #5	$86.81	4.734%	$90.9196	$90.92	$90.90	$90.90
Purchase #6	$232.27	3.280%	$239.8885	$239.89	$239.90	$239.90
Purchase #7	$128.75	8.139%	$139.229	$139.23	$139.25	$139.20
7 purchase totals =	$926.85		$988.5833	$988.58	$988.55	$988.50