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	$97.55	12.346%	$109.5935	$109.59	$109.60	$109.60
Purchase #2	$195.65	5.737%	$206.8744	$206.87	$206.85	$206.90
Purchase #3	$193.76	11.351%	$215.7537	$215.75	$215.75	$215.80
Purchase #4	$211.85	12.426%	$238.1745	$238.17	$238.15	$238.20
Purchase #5	$91.58	11.798%	$102.3846	$102.38	$102.40	$102.40
Purchase #6	$173.94	6.630%	$185.4722	$185.47	$185.45	$185.50
Purchase #7	$77.94	8.125%	$84.2726	$84.27	$84.25	$84.30
7 purchase totals =	$1,042.27		$1,142.5255	$1,142.50	$1,142.45	$1,142.70