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	$63.86	5.285%	$67.235	$67.24	$67.25	$67.20
Purchase #2	$121.73	4.859%	$127.6449	$127.64	$127.65	$127.60
Purchase #3	$36.86	13.478%	$41.828	$41.83	$41.85	$41.80
Purchase #4	$111.37	9.238%	$121.6584	$121.66	$121.65	$121.70
Purchase #5	$20.57	12.334%	$23.1071	$23.11	$23.10	$23.10
Purchase #6	$125.84	12.421%	$141.4706	$141.47	$141.45	$141.50
Purchase #7	$19.38	7.748%	$20.8816	$20.88	$20.90	$20.90
7 purchase totals =	$499.61		$543.8256	$543.83	$543.85	$543.80