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	$136.59	5.422%	$143.9959	$144.00	$144.00	$144.00
Purchase #2	$129.68	8.665%	$140.9168	$140.92	$140.90	$140.90
Purchase #3	$85.71	4.224%	$89.3304	$89.33	$89.35	$89.30
Purchase #4	$145.82	6.363%	$155.0985	$155.10	$155.10	$155.10
Purchase #5	$102.26	13.329%	$115.8902	$115.89	$115.90	$115.90
Purchase #6	$171.97	5.353%	$181.1756	$181.18	$181.20	$181.20
Purchase #7	$130.90	13.424%	$148.472	$148.47	$148.45	$148.50
7 purchase totals =	$902.93		$974.8794	$974.89	$974.90	$974.90