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	$121.91	12.830%	$137.5511	$137.55	$137.55	$137.60
Purchase #2	$186.60	5.222%	$196.3443	$196.34	$196.35	$196.30
Purchase #3	$155.39	9.664%	$170.4069	$170.41	$170.40	$170.40
Purchase #4	$9.34	13.375%	$10.5892	$10.59	$10.60	$10.60
Purchase #5	$197.60	5.217%	$207.9088	$207.91	$207.90	$207.90
Purchase #6	$185.85	7.824%	$200.3909	$200.39	$200.40	$200.40
Purchase #7	$108.71	7.354%	$116.7045	$116.70	$116.70	$116.70
7 purchase totals =	$965.40		$1,039.8957	$1,039.89	$1,039.90	$1,039.90