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	$52.94	5.671%	$55.9422	$55.94	$55.95	$55.90
Purchase #2	$128.75	11.731%	$143.8537	$143.85	$143.85	$143.90
Purchase #3	$56.26	11.199%	$62.5606	$62.56	$62.55	$62.60
Purchase #4	$76.45	11.545%	$85.2762	$85.28	$85.30	$85.30
Purchase #5	$65.29	3.703%	$67.7077	$67.71	$67.70	$67.70
Purchase #6	$173.27	4.519%	$181.1001	$181.10	$181.10	$181.10
Purchase #7	$81.65	3.588%	$84.5796	$84.58	$84.60	$84.60
7 purchase totals =	$634.61		$681.0201	$681.02	$681.05	$681.10