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	$31.38	12.748%	$35.3803	$35.38	$35.40	$35.40
Purchase #2	$141.49	12.193%	$158.7419	$158.74	$158.75	$158.70
Purchase #3	$106.30	8.569%	$115.4088	$115.41	$115.40	$115.40
Purchase #4	$200.94	3.828%	$208.632	$208.63	$208.65	$208.60
Purchase #5	$57.89	5.671%	$61.1729	$61.17	$61.15	$61.20
Purchase #6	$70.78	10.429%	$78.1616	$78.16	$78.15	$78.20
Purchase #7	$226.82	10.209%	$249.9761	$249.98	$250.00	$250.00
7 purchase totals =	$835.60		$907.4736	$907.47	$907.50	$907.50