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	$139.74	8.249%	$151.2672	$151.27	$151.25	$151.30
Purchase #2	$135.32	12.716%	$152.5273	$152.53	$152.55	$152.50
Purchase #3	$176.90	4.354%	$184.6022	$184.60	$184.60	$184.60
Purchase #4	$68.60	13.833%	$78.0894	$78.09	$78.10	$78.10
Purchase #5	$219.85	5.271%	$231.4383	$231.44	$231.45	$231.40
Purchase #6	$46.98	12.817%	$53.0014	$53.00	$53.00	$53.00
Purchase #7	$80.89	10.432%	$89.3284	$89.33	$89.35	$89.30
7 purchase totals =	$868.28		$940.2542	$940.26	$940.30	$940.20