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	$103.75	4.783%	$108.7124	$108.71	$108.70	$108.70
Purchase #2	$81.61	10.326%	$90.037	$90.04	$90.05	$90.00
Purchase #3	$177.87	10.293%	$196.1782	$196.18	$196.20	$196.20
Purchase #4	$198.65	10.318%	$219.1467	$219.15	$219.15	$219.10
Purchase #5	$40.89	7.215%	$43.8402	$43.84	$43.85	$43.80
Purchase #6	$53.25	6.691%	$56.813	$56.81	$56.80	$56.80
Purchase #7	$185.36	12.115%	$207.8164	$207.82	$207.80	$207.80
7 purchase totals =	$841.38		$922.5439	$922.55	$922.55	$922.40