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	$41.32	5.271%	$43.498	$43.50	$43.50	$43.50
Purchase #2	$33.29	7.333%	$35.7312	$35.73	$35.75	$35.70
Purchase #3	$126.74	4.585%	$132.551	$132.55	$132.55	$132.60
Purchase #4	$126.61	10.652%	$140.0965	$140.10	$140.10	$140.10
Purchase #5	$143.78	11.484%	$160.2917	$160.29	$160.30	$160.30
Purchase #6	$105.83	5.236%	$111.3713	$111.37	$111.35	$111.40
Purchase #7	$37.49	11.323%	$41.735	$41.74	$41.75	$41.70
7 purchase totals =	$615.06		$665.2747	$665.28	$665.30	$665.30