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	$13.85	10.369%	$15.2861	$15.29	$15.30	$15.30
Purchase #2	$229.98	8.583%	$249.7192	$249.72	$249.70	$249.70
Purchase #3	$14.59	5.695%	$15.4209	$15.42	$15.40	$15.40
Purchase #4	$250.39	12.127%	$280.7548	$280.75	$280.75	$280.80
Purchase #5	$187.69	13.225%	$212.512	$212.51	$212.50	$212.50
Purchase #6	$55.28	7.379%	$59.3591	$59.36	$59.35	$59.40
Purchase #7	$209.94	4.656%	$219.7148	$219.71	$219.70	$219.70
7 purchase totals =	$961.72		$1,052.7669	$1,052.76	$1,052.70	$1,052.80