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	$152.37	12.115%	$170.8296	$170.83	$170.85	$170.80
Purchase #2	$195.50	5.254%	$205.7716	$205.77	$205.75	$205.80
Purchase #3	$197.50	9.285%	$215.8379	$215.84	$215.85	$215.80
Purchase #4	$76.75	7.190%	$82.2683	$82.27	$82.25	$82.30
Purchase #5	$233.80	3.705%	$242.4623	$242.46	$242.45	$242.50
Purchase #6	$233.65	3.526%	$241.8885	$241.89	$241.90	$241.90
Purchase #7	$51.83	5.692%	$54.7802	$54.78	$54.80	$54.80
7 purchase totals =	$1,141.40		$1,213.8384	$1,213.84	$1,213.85	$1,213.90