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	$102.64	13.179%	$116.1669	$116.17	$116.15	$116.20
Purchase #2	$164.88	13.801%	$187.6351	$187.64	$187.65	$187.60
Purchase #3	$198.85	12.342%	$223.3921	$223.39	$223.40	$223.40
Purchase #4	$41.46	11.406%	$46.1889	$46.19	$46.20	$46.20
Purchase #5	$141.94	3.220%	$146.5105	$146.51	$146.50	$146.50
Purchase #6	$100.30	10.158%	$110.4885	$110.49	$110.50	$110.50
Purchase #7	$152.50	3.279%	$157.5005	$157.50	$157.50	$157.50
7 purchase totals =	$902.57		$987.8825	$987.89	$987.90	$987.90