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	$26.47	3.354%	$27.3578	$27.36	$27.35	$27.40
Purchase #2	$115.86	13.828%	$131.8811	$131.88	$131.90	$131.90
Purchase #3	$46.99	11.626%	$52.4531	$52.45	$52.45	$52.50
Purchase #4	$164.86	13.563%	$187.22	$187.22	$187.20	$187.20
Purchase #5	$223.96	9.345%	$244.8891	$244.89	$244.90	$244.90
Purchase #6	$248.98	7.228%	$266.9763	$266.98	$267.00	$267.00
Purchase #7	$68.58	5.622%	$72.4356	$72.44	$72.45	$72.40
7 purchase totals =	$895.70		$983.2130	$983.22	$983.25	$983.30