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	$22.94	4.356%	$23.9393	$23.94	$23.95	$23.90
Purchase #2	$99.47	10.356%	$109.7711	$109.77	$109.75	$109.80
Purchase #3	$85.97	4.720%	$90.0278	$90.03	$90.05	$90.00
Purchase #4	$206.60	9.265%	$225.7415	$225.74	$225.75	$225.70
Purchase #5	$99.46	11.757%	$111.1535	$111.15	$111.15	$111.20
Purchase #6	$213.49	10.249%	$235.3706	$235.37	$235.35	$235.40
Purchase #7	$225.75	3.800%	$234.3285	$234.33	$234.35	$234.30
7 purchase totals =	$953.68		$1,030.3323	$1,030.33	$1,030.35	$1,030.30