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	$18.94	8.791%	$20.605	$20.61	$20.60	$20.60
Purchase #2	$90.61	10.655%	$100.2645	$100.26	$100.25	$100.30
Purchase #3	$103.39	11.810%	$115.6004	$115.60	$115.60	$115.60
Purchase #4	$230.47	12.176%	$258.532	$258.53	$258.55	$258.50
Purchase #5	$91.37	6.106%	$96.9491	$96.95	$96.95	$96.90
Purchase #6	$219.29	12.458%	$246.6091	$246.61	$246.60	$246.60
Purchase #7	$100.71	7.635%	$108.3992	$108.40	$108.40	$108.40
7 purchase totals =	$854.78		$946.9593	$946.96	$946.95	$946.90