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	$122.72	6.849%	$131.1251	$131.13	$131.15	$131.10
Purchase #2	$234.74	4.676%	$245.7164	$245.72	$245.70	$245.70
Purchase #3	$106.25	5.793%	$112.4051	$112.41	$112.40	$112.40
Purchase #4	$104.28	7.702%	$112.3116	$112.31	$112.30	$112.30
Purchase #5	$208.78	5.866%	$221.027	$221.03	$221.05	$221.00
Purchase #6	$6.92	5.258%	$7.2839	$7.28	$7.30	$7.30
Purchase #7	$78.71	8.870%	$85.6916	$85.69	$85.70	$85.70
7 purchase totals =	$862.40		$915.5607	$915.57	$915.60	$915.50