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	$70.54	9.740%	$77.4106	$77.41	$77.40	$77.40
Purchase #2	$104.59	11.841%	$116.9745	$116.97	$116.95	$117.00
Purchase #3	$27.88	8.162%	$30.1556	$30.16	$30.15	$30.20
Purchase #4	$139.32	9.284%	$152.2545	$152.25	$152.25	$152.30
Purchase #5	$34.72	9.163%	$37.9014	$37.90	$37.90	$37.90
Purchase #6	$244.70	12.633%	$275.613	$275.61	$275.60	$275.60
Purchase #7	$135.68	3.653%	$140.6364	$140.64	$140.65	$140.60
7 purchase totals =	$757.43		$830.9460	$830.94	$830.90	$831.00