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	$50.92	8.475%	$55.2355	$55.24	$55.25	$55.20
Purchase #2	$103.95	12.441%	$116.8824	$116.88	$116.90	$116.90
Purchase #3	$103.70	5.703%	$109.614	$109.61	$109.60	$109.60
Purchase #4	$31.75	7.217%	$34.0414	$34.04	$34.05	$34.00
Purchase #5	$6.49	13.201%	$7.3467	$7.35	$7.35	$7.30
Purchase #6	$41.40	3.438%	$42.8233	$42.82	$42.80	$42.80
Purchase #7	$65.62	12.167%	$73.604	$73.60	$73.60	$73.60
7 purchase totals =	$403.83		$439.5473	$439.54	$439.55	$439.40