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	$131.29	10.660%	$145.2855	$145.29	$145.30	$145.30
Purchase #2	$167.77	6.159%	$178.103	$178.10	$178.10	$178.10
Purchase #3	$169.98	10.661%	$188.1016	$188.10	$188.10	$188.10
Purchase #4	$236.49	9.687%	$259.3988	$259.40	$259.40	$259.40
Purchase #5	$173.87	6.478%	$185.1333	$185.13	$185.15	$185.10
Purchase #6	$134.29	3.400%	$138.8559	$138.86	$138.85	$138.90
Purchase #7	$181.89	4.515%	$190.1023	$190.10	$190.10	$190.10
7 purchase totals =	$1,195.58		$1,284.9804	$1,284.98	$1,285.00	$1,285.00