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	$52.45	13.168%	$59.3566	$59.36	$59.35	$59.40
Purchase #2	$178.25	11.605%	$198.9359	$198.94	$198.95	$198.90
Purchase #3	$143.49	13.279%	$162.544	$162.54	$162.55	$162.50
Purchase #4	$55.73	8.201%	$60.3004	$60.30	$60.30	$60.30
Purchase #5	$66.40	3.834%	$68.9458	$68.95	$68.95	$68.90
Purchase #6	$62.79	10.682%	$69.4972	$69.50	$69.50	$69.50
Purchase #7	$156.75	5.149%	$164.8211	$164.82	$164.80	$164.80
7 purchase totals =	$715.86		$784.4010	$784.41	$784.40	$784.30