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	$53.59	3.741%	$55.5948	$55.59	$55.60	$55.60
Purchase #2	$218.84	6.548%	$233.1696	$233.17	$233.15	$233.20
Purchase #3	$236.47	9.272%	$258.3955	$258.40	$258.40	$258.40
Purchase #4	$152.51	6.287%	$162.0983	$162.10	$162.10	$162.10
Purchase #5	$28.55	12.205%	$32.0345	$32.03	$32.05	$32.00
Purchase #6	$213.92	5.386%	$225.4417	$225.44	$225.45	$225.40
Purchase #7	$242.50	8.481%	$263.0664	$263.07	$263.05	$263.10
7 purchase totals =	$1,146.38		$1,229.8008	$1,229.80	$1,229.80	$1,229.80