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	$78.50	9.318%	$85.8146	$85.81	$85.80	$85.80
Purchase #2	$221.67	11.339%	$246.8052	$246.81	$246.80	$246.80
Purchase #3	$54.94	12.680%	$61.9064	$61.91	$61.90	$61.90
Purchase #4	$88.27	8.611%	$95.8709	$95.87	$95.85	$95.90
Purchase #5	$79.61	4.145%	$82.9098	$82.91	$82.90	$82.90
Purchase #6	$8.66	10.831%	$9.598	$9.60	$9.60	$9.60
Purchase #7	$84.57	7.704%	$91.0853	$91.09	$91.10	$91.10
7 purchase totals =	$616.22		$673.9902	$674.00	$673.95	$674.00