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	$222.68	6.244%	$236.5841	$236.58	$236.60	$236.60
Purchase #2	$185.28	12.198%	$207.8805	$207.88	$207.90	$207.90
Purchase #3	$100.72	4.682%	$105.4357	$105.44	$105.45	$105.40
Purchase #4	$90.71	11.652%	$101.2795	$101.28	$101.30	$101.30
Purchase #5	$156.25	10.590%	$172.7969	$172.80	$172.80	$172.80
Purchase #6	$228.98	7.520%	$246.1993	$246.20	$246.20	$246.20
Purchase #7	$91.94	11.238%	$102.2722	$102.27	$102.25	$102.30
7 purchase totals =	$1,076.56		$1,172.4482	$1,172.45	$1,172.50	$1,172.50