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	$201.53	10.635%	$222.9627	$222.96	$222.95	$223.00
Purchase #2	$35.45	13.392%	$40.1975	$40.20	$40.20	$40.20
Purchase #3	$95.80	3.816%	$99.4557	$99.46	$99.45	$99.50
Purchase #4	$184.51	7.525%	$198.3944	$198.39	$198.40	$198.40
Purchase #5	$131.77	9.255%	$143.9653	$143.97	$143.95	$144.00
Purchase #6	$48.27	7.434%	$51.8584	$51.86	$51.85	$51.90
Purchase #7	$31.79	4.241%	$33.1382	$33.14	$33.15	$33.10
7 purchase totals =	$729.12		$789.9722	$789.98	$789.95	$790.10