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	$157.72	7.740%	$169.9275	$169.93	$169.95	$169.90
Purchase #2	$141.66	11.780%	$158.3475	$158.35	$158.35	$158.30
Purchase #3	$248.81	10.444%	$274.7957	$274.80	$274.80	$274.80
Purchase #4	$18.35	11.154%	$20.3968	$20.40	$20.40	$20.40
Purchase #5	$103.32	13.775%	$117.5523	$117.55	$117.55	$117.60
Purchase #6	$150.91	4.607%	$157.8624	$157.86	$157.85	$157.90
Purchase #7	$87.94	3.348%	$90.8842	$90.88	$90.90	$90.90
7 purchase totals =	$908.71		$989.7664	$989.77	$989.80	$989.80