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	$76.39	8.536%	$82.9107	$82.91	$82.90	$82.90
Purchase #2	$202.72	5.224%	$213.3101	$213.31	$213.30	$213.30
Purchase #3	$39.91	6.111%	$42.3489	$42.35	$42.35	$42.30
Purchase #4	$32.49	4.425%	$33.9277	$33.93	$33.95	$33.90
Purchase #5	$203.79	9.363%	$222.8709	$222.87	$222.85	$222.90
Purchase #6	$230.35	8.116%	$249.0452	$249.05	$249.05	$249.00
Purchase #7	$229.48	11.110%	$254.9752	$254.98	$255.00	$255.00
7 purchase totals =	$1,015.13		$1,099.3887	$1,099.40	$1,099.40	$1,099.30