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	$235.73	9.274%	$257.5916	$257.59	$257.60	$257.60
Purchase #2	$29.77	4.732%	$31.1787	$31.18	$31.20	$31.20
Purchase #3	$6.33	8.751%	$6.8839	$6.88	$6.90	$6.90
Purchase #4	$99.83	9.134%	$108.9485	$108.95	$108.95	$108.90
Purchase #5	$73.81	6.726%	$78.7745	$78.77	$78.75	$78.80
Purchase #6	$118.29	8.608%	$128.4724	$128.47	$128.45	$128.50
Purchase #7	$106.96	9.809%	$117.4517	$117.45	$117.45	$117.50
7 purchase totals =	$670.72		$729.3013	$729.29	$729.30	$729.40