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	$214.78	7.568%	$231.0346	$231.03	$231.05	$231.00
Purchase #2	$146.70	13.728%	$166.839	$166.84	$166.85	$166.80
Purchase #3	$210.32	7.738%	$226.5946	$226.59	$226.60	$226.60
Purchase #4	$102.74	12.794%	$115.8846	$115.88	$115.90	$115.90
Purchase #5	$167.28	8.265%	$181.1057	$181.11	$181.10	$181.10
Purchase #6	$69.27	13.806%	$78.8334	$78.83	$78.85	$78.80
Purchase #7	$120.59	8.814%	$131.2188	$131.22	$131.20	$131.20
7 purchase totals =	$1,031.68		$1,131.5107	$1,131.50	$1,131.55	$1,131.40