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	$13.70	12.122%	$15.3607	$15.36	$15.35	$15.40
Purchase #2	$13.86	5.409%	$14.6097	$14.61	$14.60	$14.60
Purchase #3	$231.44	10.548%	$255.8523	$255.85	$255.85	$255.90
Purchase #4	$47.69	11.759%	$53.2979	$53.30	$53.30	$53.30
Purchase #5	$93.35	3.161%	$96.3008	$96.30	$96.30	$96.30
Purchase #6	$42.63	12.421%	$47.9251	$47.93	$47.95	$47.90
Purchase #7	$116.33	12.665%	$131.0632	$131.06	$131.05	$131.10
7 purchase totals =	$559.00		$614.4097	$614.41	$614.40	$614.50