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	$78.60	13.347%	$89.0907	$89.09	$89.10	$89.10
Purchase #2	$121.53	13.790%	$138.289	$138.29	$138.30	$138.30
Purchase #3	$40.67	5.767%	$43.0154	$43.02	$43.00	$43.00
Purchase #4	$39.87	6.853%	$42.6023	$42.60	$42.60	$42.60
Purchase #5	$235.37	5.756%	$248.9179	$248.92	$248.90	$248.90
Purchase #6	$56.30	10.514%	$62.2194	$62.22	$62.20	$62.20
Purchase #7	$150.46	9.747%	$165.1253	$165.13	$165.15	$165.10
7 purchase totals =	$722.80		$789.2600	$789.27	$789.25	$789.20