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	$129.80	7.474%	$139.5013	$139.50	$139.50	$139.50
Purchase #2	$242.64	12.840%	$273.795	$273.80	$273.80	$273.80
Purchase #3	$164.55	5.848%	$174.1729	$174.17	$174.15	$174.20
Purchase #4	$108.30	8.326%	$117.3171	$117.32	$117.30	$117.30
Purchase #5	$54.27	4.296%	$56.6014	$56.60	$56.60	$56.60
Purchase #6	$165.93	12.600%	$186.8372	$186.84	$186.85	$186.80
Purchase #7	$143.63	5.702%	$151.8198	$151.82	$151.80	$151.80
7 purchase totals =	$1,009.12		$1,100.0447	$1,100.05	$1,100.00	$1,100.00