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	$147.91	12.158%	$165.8929	$165.89	$165.90	$165.90
Purchase #2	$67.68	7.739%	$72.9178	$72.92	$72.90	$72.90
Purchase #3	$186.84	9.451%	$204.4982	$204.50	$204.50	$204.50
Purchase #4	$70.29	11.481%	$78.36	$78.36	$78.35	$78.40
Purchase #5	$143.58	6.833%	$153.3908	$153.39	$153.40	$153.40
Purchase #6	$46.69	12.380%	$52.4702	$52.47	$52.45	$52.50
Purchase #7	$120.88	9.874%	$132.8157	$132.82	$132.80	$132.80
7 purchase totals =	$783.87		$860.3456	$860.35	$860.30	$860.40