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	$64.29	6.693%	$68.5929	$68.59	$68.60	$68.60
Purchase #2	$217.94	4.814%	$228.4316	$228.43	$228.45	$228.40
Purchase #3	$182.83	6.624%	$194.9407	$194.94	$194.95	$194.90
Purchase #4	$142.73	12.365%	$160.3786	$160.38	$160.40	$160.40
Purchase #5	$82.82	3.341%	$85.587	$85.59	$85.60	$85.60
Purchase #6	$55.30	11.870%	$61.8641	$61.86	$61.85	$61.90
Purchase #7	$41.47	3.230%	$42.8095	$42.81	$42.80	$42.80
7 purchase totals =	$787.38		$842.6044	$842.60	$842.65	$842.60