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	$76.90	9.413%	$84.1386	$84.14	$84.15	$84.10
Purchase #2	$184.66	4.450%	$192.8774	$192.88	$192.90	$192.90
Purchase #3	$53.60	10.699%	$59.3347	$59.33	$59.35	$59.30
Purchase #4	$158.41	13.584%	$179.9284	$179.93	$179.95	$179.90
Purchase #5	$132.47	10.719%	$146.6695	$146.67	$146.65	$146.70
Purchase #6	$201.89	10.534%	$223.1571	$223.16	$223.15	$223.20
Purchase #7	$131.79	7.102%	$141.1497	$141.15	$141.15	$141.10
7 purchase totals =	$939.72		$1,027.2554	$1,027.26	$1,027.30	$1,027.20