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	$38.55	6.827%	$41.1818	$41.18	$41.20	$41.20
Purchase #2	$82.84	8.459%	$89.8474	$89.85	$89.85	$89.80
Purchase #3	$238.97	4.678%	$250.149	$250.15	$250.15	$250.10
Purchase #4	$17.34	6.849%	$18.5276	$18.53	$18.55	$18.50
Purchase #5	$213.31	5.302%	$224.6197	$224.62	$224.60	$224.60
Purchase #6	$133.59	7.155%	$143.1484	$143.15	$143.15	$143.10
Purchase #7	$129.40	12.468%	$145.5336	$145.53	$145.55	$145.50
7 purchase totals =	$854.00		$913.0075	$913.01	$913.05	$912.80