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	$64.92	11.865%	$72.6228	$72.62	$72.60	$72.60
Purchase #2	$161.87	5.628%	$170.98	$170.98	$171.00	$171.00
Purchase #3	$81.73	8.712%	$88.8503	$88.85	$88.85	$88.90
Purchase #4	$41.79	3.793%	$43.3751	$43.38	$43.40	$43.40
Purchase #5	$80.83	13.472%	$91.7194	$91.72	$91.70	$91.70
Purchase #6	$94.35	7.534%	$101.4583	$101.46	$101.45	$101.50
Purchase #7	$114.66	7.664%	$123.4475	$123.45	$123.45	$123.40
7 purchase totals =	$640.15		$692.4534	$692.46	$692.45	$692.50