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	$86.57	5.643%	$91.4551	$91.46	$91.45	$91.50
Purchase #2	$85.34	7.861%	$92.0486	$92.05	$92.05	$92.00
Purchase #3	$106.48	10.390%	$117.5433	$117.54	$117.55	$117.50
Purchase #4	$28.71	12.585%	$32.3232	$32.32	$32.30	$32.30
Purchase #5	$161.71	13.109%	$182.9086	$182.91	$182.90	$182.90
Purchase #6	$97.59	13.760%	$111.0184	$111.02	$111.00	$111.00
Purchase #7	$213.45	8.385%	$231.3478	$231.35	$231.35	$231.30
7 purchase totals =	$779.85		$858.6450	$858.65	$858.60	$858.50