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	$35.67	11.268%	$39.6893	$39.69	$39.70	$39.70
Purchase #2	$76.74	6.861%	$82.0051	$82.01	$82.00	$82.00
Purchase #3	$217.32	10.439%	$240.006	$240.01	$240.00	$240.00
Purchase #4	$25.74	9.599%	$28.2108	$28.21	$28.20	$28.20
Purchase #5	$173.49	7.542%	$186.5746	$186.57	$186.55	$186.60
Purchase #6	$50.86	3.549%	$52.665	$52.67	$52.65	$52.70
Purchase #7	$37.83	6.580%	$40.3192	$40.32	$40.30	$40.30
7 purchase totals =	$617.65		$669.4700	$669.48	$669.40	$669.50