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	$138.33	8.623%	$150.2582	$150.26	$150.25	$150.30
Purchase #2	$93.50	5.862%	$98.981	$98.98	$99.00	$99.00
Purchase #3	$32.96	12.249%	$36.9973	$37.00	$37.00	$37.00
Purchase #4	$148.51	11.766%	$165.9837	$165.98	$166.00	$166.00
Purchase #5	$175.31	9.465%	$191.9031	$191.90	$191.90	$191.90
Purchase #6	$226.96	13.273%	$257.0844	$257.08	$257.10	$257.10
Purchase #7	$55.91	10.202%	$61.6139	$61.61	$61.60	$61.60
7 purchase totals =	$871.48		$962.8216	$962.81	$962.85	$962.90