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	$151.40	8.452%	$164.1963	$164.20	$164.20	$164.20
Purchase #2	$59.78	13.627%	$67.9262	$67.93	$67.95	$67.90
Purchase #3	$90.32	10.552%	$99.8506	$99.85	$99.85	$99.90
Purchase #4	$85.54	11.640%	$95.4969	$95.50	$95.50	$95.50
Purchase #5	$108.95	3.653%	$112.9299	$112.93	$112.95	$112.90
Purchase #6	$241.83	5.112%	$254.1923	$254.19	$254.20	$254.20
Purchase #7	$194.98	4.854%	$204.4443	$204.44	$204.45	$204.40
7 purchase totals =	$932.80		$999.0365	$999.04	$999.10	$999.00