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	$233.69	10.604%	$258.4705	$258.47	$258.45	$258.50
Purchase #2	$73.78	12.652%	$83.1146	$83.11	$83.10	$83.10
Purchase #3	$152.25	10.307%	$167.9424	$167.94	$167.95	$167.90
Purchase #4	$179.86	9.597%	$197.1212	$197.12	$197.10	$197.10
Purchase #5	$39.51	5.732%	$41.7747	$41.77	$41.75	$41.80
Purchase #6	$149.64	4.174%	$155.886	$155.89	$155.90	$155.90
Purchase #7	$55.78	11.650%	$62.2784	$62.28	$62.30	$62.30
7 purchase totals =	$884.51		$966.5878	$966.58	$966.55	$966.60