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	$80.94	11.840%	$90.5233	$90.52	$90.50	$90.50
Purchase #2	$238.43	6.809%	$254.6647	$254.66	$254.65	$254.70
Purchase #3	$162.93	6.184%	$173.0056	$173.01	$173.00	$173.00
Purchase #4	$156.97	6.641%	$167.3944	$167.39	$167.40	$167.40
Purchase #5	$91.37	9.367%	$99.9286	$99.93	$99.95	$99.90
Purchase #6	$176.68	12.258%	$198.3374	$198.34	$198.35	$198.30
Purchase #7	$85.73	6.715%	$91.4868	$91.49	$91.50	$91.50
7 purchase totals =	$993.05		$1,075.3408	$1,075.34	$1,075.35	$1,075.30