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	$137.36	6.361%	$146.0975	$146.10	$146.10	$146.10
Purchase #2	$133.95	12.422%	$150.5893	$150.59	$150.60	$150.60
Purchase #3	$103.77	5.789%	$109.7772	$109.78	$109.80	$109.80
Purchase #4	$231.27	11.486%	$257.8337	$257.83	$257.85	$257.80
Purchase #5	$242.41	11.588%	$270.5005	$270.50	$270.50	$270.50
Purchase #6	$158.32	4.351%	$165.2085	$165.21	$165.20	$165.20
Purchase #7	$174.60	7.411%	$187.5396	$187.54	$187.55	$187.50
7 purchase totals =	$1,181.68		$1,287.5463	$1,287.55	$1,287.60	$1,287.50