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	$175.89	8.264%	$190.4255	$190.43	$190.45	$190.40
Purchase #2	$166.41	4.492%	$173.8851	$173.89	$173.90	$173.90
Purchase #3	$163.44	12.806%	$184.3701	$184.37	$184.35	$184.40
Purchase #4	$211.46	13.280%	$239.5419	$239.54	$239.55	$239.50
Purchase #5	$8.37	13.357%	$9.488	$9.49	$9.50	$9.50
Purchase #6	$69.29	13.763%	$78.8264	$78.83	$78.85	$78.80
Purchase #7	$58.64	11.315%	$65.2751	$65.28	$65.30	$65.30
7 purchase totals =	$853.50		$941.8121	$941.83	$941.90	$941.80