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	$26.66	3.560%	$27.6091	$27.61	$27.60	$27.60
Purchase #2	$182.79	3.571%	$189.3174	$189.32	$189.30	$189.30
Purchase #3	$134.56	7.719%	$144.9467	$144.95	$144.95	$144.90
Purchase #4	$206.92	10.316%	$228.2659	$228.27	$228.25	$228.30
Purchase #5	$217.59	11.447%	$242.4975	$242.50	$242.50	$242.50
Purchase #6	$102.77	8.816%	$111.8302	$111.83	$111.85	$111.80
Purchase #7	$89.66	6.256%	$95.2691	$95.27	$95.25	$95.30
7 purchase totals =	$960.95		$1,039.7359	$1,039.75	$1,039.70	$1,039.70