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	$11.87	3.739%	$12.3138	$12.31	$12.30	$12.30
Purchase #2	$104.27	12.646%	$117.456	$117.46	$117.45	$117.50
Purchase #3	$78.60	10.590%	$86.9237	$86.92	$86.90	$86.90
Purchase #4	$73.76	6.761%	$78.7469	$78.75	$78.75	$78.70
Purchase #5	$174.30	10.196%	$192.0716	$192.07	$192.05	$192.10
Purchase #6	$134.37	7.853%	$144.9221	$144.92	$144.90	$144.90
Purchase #7	$185.69	10.649%	$205.4641	$205.46	$205.45	$205.50
7 purchase totals =	$762.86		$837.8982	$837.89	$837.80	$837.90