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	$5.58	10.779%	$6.1815	$6.18	$6.20	$6.20
Purchase #2	$14.38	7.605%	$15.4736	$15.47	$15.45	$15.50
Purchase #3	$64.65	11.245%	$71.9199	$71.92	$71.90	$71.90
Purchase #4	$151.70	11.321%	$168.874	$168.87	$168.85	$168.90
Purchase #5	$12.44	3.503%	$12.8758	$12.88	$12.90	$12.90
Purchase #6	$69.90	12.289%	$78.49	$78.49	$78.50	$78.50
Purchase #7	$77.35	5.225%	$81.3915	$81.39	$81.40	$81.40
7 purchase totals =	$396.00		$435.2063	$435.20	$435.20	$435.30