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	$87.89	11.865%	$98.3181	$98.32	$98.30	$98.30
Purchase #2	$6.84	10.508%	$7.5587	$7.56	$7.55	$7.60
Purchase #3	$122.42	6.873%	$130.8339	$130.83	$130.85	$130.80
Purchase #4	$213.59	8.141%	$230.9784	$230.98	$231.00	$231.00
Purchase #5	$108.78	13.103%	$123.0334	$123.03	$123.05	$123.00
Purchase #6	$230.75	4.779%	$241.7775	$241.78	$241.80	$241.80
Purchase #7	$10.43	4.112%	$10.8589	$10.86	$10.85	$10.90
7 purchase totals =	$780.70		$843.3589	$843.36	$843.40	$843.40