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	$41.76	3.107%	$43.0575	$43.06	$43.05	$43.10
Purchase #2	$98.78	13.731%	$112.3435	$112.34	$112.35	$112.30
Purchase #3	$117.44	8.434%	$127.3449	$127.34	$127.35	$127.30
Purchase #4	$133.69	11.252%	$148.7328	$148.73	$148.75	$148.70
Purchase #5	$132.90	13.236%	$150.4906	$150.49	$150.50	$150.50
Purchase #6	$222.92	8.703%	$242.3207	$242.32	$242.30	$242.30
Purchase #7	$81.43	13.789%	$92.6584	$92.66	$92.65	$92.70
7 purchase totals =	$828.92		$916.9484	$916.94	$916.95	$916.90