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	$141.36	8.586%	$153.4972	$153.50	$153.50	$153.50
Purchase #2	$208.77	12.343%	$234.5385	$234.54	$234.55	$234.50
Purchase #3	$11.53	3.699%	$11.9565	$11.96	$11.95	$12.00
Purchase #4	$239.47	13.376%	$271.5015	$271.50	$271.50	$271.50
Purchase #5	$111.34	7.850%	$120.0802	$120.08	$120.10	$120.10
Purchase #6	$59.44	10.861%	$65.8958	$65.90	$65.90	$65.90
Purchase #7	$115.96	4.192%	$120.821	$120.82	$120.80	$120.80
7 purchase totals =	$887.87		$978.2907	$978.30	$978.30	$978.30