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	$169.50	8.694%	$184.2363	$184.24	$184.25	$184.20
Purchase #2	$239.33	8.176%	$258.8976	$258.90	$258.90	$258.90
Purchase #3	$129.84	11.544%	$144.8287	$144.83	$144.85	$144.80
Purchase #4	$139.43	10.625%	$154.2444	$154.24	$154.25	$154.20
Purchase #5	$77.87	10.297%	$85.8883	$85.89	$85.90	$85.90
Purchase #6	$32.27	7.631%	$34.7325	$34.73	$34.75	$34.70
Purchase #7	$124.50	5.651%	$131.5355	$131.54	$131.55	$131.50
7 purchase totals =	$912.74		$994.3633	$994.37	$994.45	$994.20