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	$85.29	6.113%	$90.5038	$90.50	$90.50	$90.50
Purchase #2	$244.50	10.303%	$269.6908	$269.69	$269.70	$269.70
Purchase #3	$85.47	7.697%	$92.0486	$92.05	$92.05	$92.00
Purchase #4	$62.40	5.630%	$65.9131	$65.91	$65.90	$65.90
Purchase #5	$197.93	12.132%	$221.9429	$221.94	$221.95	$221.90
Purchase #6	$175.65	5.842%	$185.9115	$185.91	$185.90	$185.90
Purchase #7	$19.28	3.592%	$19.9725	$19.97	$19.95	$20.00
7 purchase totals =	$870.52		$945.9832	$945.97	$945.95	$945.90