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	$127.47	6.666%	$135.9672	$135.97	$135.95	$136.00
Purchase #2	$98.28	4.761%	$102.9591	$102.96	$102.95	$103.00
Purchase #3	$155.38	9.538%	$170.2001	$170.20	$170.20	$170.20
Purchase #4	$187.76	4.857%	$196.8795	$196.88	$196.90	$196.90
Purchase #5	$167.67	3.228%	$173.0824	$173.08	$173.10	$173.10
Purchase #6	$49.62	11.829%	$55.4895	$55.49	$55.50	$55.50
Purchase #7	$90.88	9.348%	$99.3755	$99.38	$99.40	$99.40
7 purchase totals =	$877.06		$933.9533	$933.96	$934.00	$934.10