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	$72.97	12.812%	$82.3189	$82.32	$82.30	$82.30
Purchase #2	$95.75	3.632%	$99.2276	$99.23	$99.25	$99.20
Purchase #3	$138.51	7.174%	$148.4467	$148.45	$148.45	$148.40
Purchase #4	$80.95	4.255%	$84.3944	$84.39	$84.40	$84.40
Purchase #5	$165.62	8.629%	$179.9113	$179.91	$179.90	$179.90
Purchase #6	$32.81	9.221%	$35.8354	$35.84	$35.85	$35.80
Purchase #7	$172.94	8.402%	$187.4704	$187.47	$187.45	$187.50
7 purchase totals =	$759.55		$817.6047	$817.61	$817.60	$817.50