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	$49.35	3.632%	$51.1424	$51.14	$51.15	$51.10
Purchase #2	$230.73	8.750%	$250.9189	$250.92	$250.90	$250.90
Purchase #3	$80.86	6.783%	$86.3447	$86.34	$86.35	$86.30
Purchase #4	$183.34	7.321%	$196.7623	$196.76	$196.75	$196.80
Purchase #5	$62.76	11.367%	$69.8939	$69.89	$69.90	$69.90
Purchase #6	$212.85	9.413%	$232.8856	$232.89	$232.90	$232.90
Purchase #7	$95.30	7.578%	$102.5218	$102.52	$102.50	$102.50
7 purchase totals =	$915.19		$990.4696	$990.46	$990.45	$990.40