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	$128.89	7.157%	$138.1147	$138.11	$138.10	$138.10
Purchase #2	$190.95	9.128%	$208.3799	$208.38	$208.40	$208.40
Purchase #3	$172.88	13.813%	$196.7599	$196.76	$196.75	$196.80
Purchase #4	$95.77	5.134%	$100.6868	$100.69	$100.70	$100.70
Purchase #5	$238.50	13.213%	$270.013	$270.01	$270.00	$270.00
Purchase #6	$222.55	7.762%	$239.8243	$239.82	$239.80	$239.80
Purchase #7	$131.57	9.219%	$143.6994	$143.70	$143.70	$143.70
7 purchase totals =	$1,181.11		$1,297.4780	$1,297.47	$1,297.45	$1,297.50