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	$142.30	5.477%	$150.0938	$150.09	$150.10	$150.10
Purchase #2	$210.32	13.853%	$239.4556	$239.46	$239.45	$239.50
Purchase #3	$88.64	12.767%	$99.9567	$99.96	$99.95	$100.00
Purchase #4	$19.91	4.871%	$20.8798	$20.88	$20.90	$20.90
Purchase #5	$72.62	7.210%	$77.8559	$77.86	$77.85	$77.90
Purchase #6	$30.64	6.435%	$32.6117	$32.61	$32.60	$32.60
Purchase #7	$135.82	12.166%	$152.3439	$152.34	$152.35	$152.30
7 purchase totals =	$700.25		$773.1974	$773.20	$773.20	$773.30