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	$222.43	12.206%	$249.5798	$249.58	$249.60	$249.60
Purchase #2	$74.97	11.836%	$83.8434	$83.84	$83.85	$83.80
Purchase #3	$29.32	9.402%	$32.0767	$32.08	$32.10	$32.10
Purchase #4	$49.68	4.681%	$52.0055	$52.01	$52.00	$52.00
Purchase #5	$57.80	3.231%	$59.6675	$59.67	$59.65	$59.70
Purchase #6	$45.50	12.459%	$51.1688	$51.17	$51.15	$51.20
Purchase #7	$82.75	8.173%	$89.5132	$89.51	$89.50	$89.50
7 purchase totals =	$562.45		$617.8549	$617.86	$617.85	$617.90