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	$23.29	4.236%	$24.2766	$24.28	$24.30	$24.30
Purchase #2	$225.47	3.141%	$232.552	$232.55	$232.55	$232.60
Purchase #3	$200.52	6.615%	$213.7844	$213.78	$213.80	$213.80
Purchase #4	$99.67	3.359%	$103.0179	$103.02	$103.00	$103.00
Purchase #5	$195.33	12.828%	$220.3869	$220.39	$220.40	$220.40
Purchase #6	$99.76	5.509%	$105.2558	$105.26	$105.25	$105.30
Purchase #7	$63.85	13.270%	$72.3229	$72.32	$72.30	$72.30
7 purchase totals =	$907.89		$971.5965	$971.60	$971.60	$971.70