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	$243.31	5.126%	$255.7821	$255.78	$255.80	$255.80
Purchase #2	$218.98	8.719%	$238.0729	$238.07	$238.05	$238.10
Purchase #3	$105.59	11.869%	$118.1225	$118.12	$118.10	$118.10
Purchase #4	$128.68	11.175%	$143.06	$143.06	$143.05	$143.10
Purchase #5	$65.28	12.307%	$73.314	$73.31	$73.30	$73.30
Purchase #6	$142.71	5.112%	$150.0053	$150.01	$150.00	$150.00
Purchase #7	$229.58	13.184%	$259.8478	$259.85	$259.85	$259.80
7 purchase totals =	$1,134.13		$1,238.2046	$1,238.20	$1,238.15	$1,238.20