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	$51.27	5.800%	$54.2437	$54.24	$54.25	$54.20
Purchase #2	$196.56	11.361%	$218.8912	$218.89	$218.90	$218.90
Purchase #3	$226.47	5.526%	$238.9847	$238.98	$239.00	$239.00
Purchase #4	$69.73	4.369%	$72.7765	$72.78	$72.80	$72.80
Purchase #5	$14.83	7.143%	$15.8893	$15.89	$15.90	$15.90
Purchase #6	$61.93	10.214%	$68.2555	$68.26	$68.25	$68.30
Purchase #7	$214.46	13.255%	$242.8867	$242.89	$242.90	$242.90
7 purchase totals =	$835.25		$911.9276	$911.93	$912.00	$912.00