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	$71.29	9.858%	$78.3178	$78.32	$78.30	$78.30
Purchase #2	$170.30	4.625%	$178.1764	$178.18	$178.20	$178.20
Purchase #3	$31.46	8.392%	$34.1001	$34.10	$34.10	$34.10
Purchase #4	$126.61	11.509%	$141.1815	$141.18	$141.20	$141.20
Purchase #5	$174.91	12.597%	$196.9434	$196.94	$196.95	$196.90
Purchase #6	$105.41	11.702%	$117.7451	$117.75	$117.75	$117.70
Purchase #7	$140.54	13.649%	$159.7223	$159.72	$159.70	$159.70
7 purchase totals =	$820.52		$906.1866	$906.19	$906.20	$906.10