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	$52.78	11.604%	$58.9046	$58.90	$58.90	$58.90
Purchase #2	$125.29	12.239%	$140.6242	$140.62	$140.60	$140.60
Purchase #3	$70.38	9.517%	$77.0781	$77.08	$77.10	$77.10
Purchase #4	$41.96	7.849%	$45.2534	$45.25	$45.25	$45.30
Purchase #5	$179.38	11.297%	$199.6446	$199.64	$199.65	$199.60
Purchase #6	$186.56	5.241%	$196.3376	$196.34	$196.35	$196.30
Purchase #7	$216.31	6.671%	$230.74	$230.74	$230.75	$230.70
7 purchase totals =	$872.66		$948.5825	$948.57	$948.60	$948.50