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	$99.26	4.497%	$103.7237	$103.72	$103.70	$103.70
Purchase #2	$120.83	13.821%	$137.5299	$137.53	$137.55	$137.50
Purchase #3	$156.27	11.685%	$174.5301	$174.53	$174.55	$174.50
Purchase #4	$104.45	13.127%	$118.1612	$118.16	$118.15	$118.20
Purchase #5	$101.34	7.109%	$108.5443	$108.54	$108.55	$108.50
Purchase #6	$216.78	10.694%	$239.9625	$239.96	$239.95	$240.00
Purchase #7	$26.50	12.813%	$29.8954	$29.90	$29.90	$29.90
7 purchase totals =	$825.43		$912.3471	$912.34	$912.35	$912.30