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	$41.86	9.126%	$45.6801	$45.68	$45.70	$45.70
Purchase #2	$129.68	12.437%	$145.8083	$145.81	$145.80	$145.80
Purchase #3	$145.81	6.261%	$154.9392	$154.94	$154.95	$154.90
Purchase #4	$225.31	6.284%	$239.4685	$239.47	$239.45	$239.50
Purchase #5	$177.59	10.633%	$196.4731	$196.47	$196.45	$196.50
Purchase #6	$83.57	5.654%	$88.295	$88.30	$88.30	$88.30
Purchase #7	$103.59	13.179%	$117.2421	$117.24	$117.25	$117.20
7 purchase totals =	$907.41		$987.9063	$987.91	$987.90	$987.90