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	$127.89	12.455%	$143.8187	$143.82	$143.80	$143.80
Purchase #2	$93.55	9.858%	$102.7722	$102.77	$102.75	$102.80
Purchase #3	$181.77	13.751%	$206.7652	$206.77	$206.75	$206.80
Purchase #4	$104.71	6.128%	$111.1266	$111.13	$111.15	$111.10
Purchase #5	$12.60	7.841%	$13.588	$13.59	$13.60	$13.60
Purchase #6	$18.64	11.175%	$20.723	$20.72	$20.70	$20.70
Purchase #7	$143.95	5.529%	$151.909	$151.91	$151.90	$151.90
7 purchase totals =	$683.11		$750.7027	$750.71	$750.65	$750.70