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	$22.75	7.715%	$24.5052	$24.51	$24.50	$24.50
Purchase #2	$142.82	10.530%	$157.8589	$157.86	$157.85	$157.90
Purchase #3	$80.76	9.345%	$88.307	$88.31	$88.30	$88.30
Purchase #4	$182.98	7.363%	$196.4528	$196.45	$196.45	$196.50
Purchase #5	$246.78	4.698%	$258.3737	$258.37	$258.35	$258.40
Purchase #6	$75.66	3.174%	$78.0614	$78.06	$78.05	$78.10
Purchase #7	$79.57	5.702%	$84.1071	$84.11	$84.10	$84.10
7 purchase totals =	$831.32		$887.6661	$887.67	$887.60	$887.80