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	$24.79	10.855%	$27.481	$27.48	$27.50	$27.50
Purchase #2	$20.74	3.548%	$21.4759	$21.48	$21.50	$21.50
Purchase #3	$32.78	6.447%	$34.8933	$34.89	$34.90	$34.90
Purchase #4	$225.72	7.793%	$243.3104	$243.31	$243.30	$243.30
Purchase #5	$72.83	4.527%	$76.127	$76.13	$76.15	$76.10
Purchase #6	$49.78	10.433%	$54.9735	$54.97	$54.95	$55.00
Purchase #7	$7.86	3.616%	$8.1442	$8.14	$8.15	$8.10
7 purchase totals =	$434.50		$466.4053	$466.40	$466.45	$466.40