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	$106.78	4.669%	$111.7656	$111.77	$111.75	$111.80
Purchase #2	$153.86	9.477%	$168.4413	$168.44	$168.45	$168.40
Purchase #3	$213.88	10.751%	$236.8742	$236.87	$236.85	$236.90
Purchase #4	$80.79	12.338%	$90.7579	$90.76	$90.75	$90.80
Purchase #5	$119.67	9.698%	$131.2756	$131.28	$131.30	$131.30
Purchase #6	$31.52	4.146%	$32.8268	$32.83	$32.85	$32.80
Purchase #7	$61.71	3.188%	$63.6773	$63.68	$63.70	$63.70
7 purchase totals =	$768.21		$835.6187	$835.63	$835.65	$835.70