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	$220.76	8.845%	$240.2862	$240.29	$240.30	$240.30
Purchase #2	$86.30	5.419%	$90.9766	$90.98	$91.00	$91.00
Purchase #3	$102.32	8.336%	$110.8494	$110.85	$110.85	$110.80
Purchase #4	$7.46	13.455%	$8.4637	$8.46	$8.45	$8.50
Purchase #5	$250.84	12.513%	$282.2276	$282.23	$282.25	$282.20
Purchase #6	$76.58	11.585%	$85.4518	$85.45	$85.45	$85.50
Purchase #7	$186.55	7.494%	$200.5301	$200.53	$200.55	$200.50
7 purchase totals =	$930.81		$1,018.7854	$1,018.79	$1,018.85	$1,018.80