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	$233.85	5.603%	$246.9526	$246.95	$246.95	$247.00
Purchase #2	$119.89	11.290%	$133.4256	$133.43	$133.45	$133.40
Purchase #3	$197.54	13.249%	$223.7121	$223.71	$223.70	$223.70
Purchase #4	$109.57	7.443%	$117.7253	$117.73	$117.75	$117.70
Purchase #5	$176.80	4.838%	$185.3536	$185.35	$185.35	$185.40
Purchase #6	$219.52	4.244%	$228.8364	$228.84	$228.85	$228.80
Purchase #7	$99.58	6.270%	$105.8237	$105.82	$105.80	$105.80
7 purchase totals =	$1,156.75		$1,241.8293	$1,241.83	$1,241.85	$1,241.80