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	$86.82	13.559%	$98.5919	$98.59	$98.60	$98.60
Purchase #2	$115.36	12.736%	$130.0522	$130.05	$130.05	$130.10
Purchase #3	$116.54	9.332%	$127.4155	$127.42	$127.40	$127.40
Purchase #4	$191.50	13.428%	$217.2146	$217.21	$217.20	$217.20
Purchase #5	$146.50	5.402%	$154.4139	$154.41	$154.40	$154.40
Purchase #6	$211.83	13.469%	$240.3614	$240.36	$240.35	$240.40
Purchase #7	$30.94	4.340%	$32.2828	$32.28	$32.30	$32.30
7 purchase totals =	$899.49		$1,000.3323	$1,000.32	$1,000.30	$1,000.40