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	$128.78	12.834%	$145.3076	$145.31	$145.30	$145.30
Purchase #2	$225.30	10.347%	$248.6118	$248.61	$248.60	$248.60
Purchase #3	$109.75	11.161%	$121.9992	$122.00	$122.00	$122.00
Purchase #4	$196.35	13.483%	$222.8239	$222.82	$222.80	$222.80
Purchase #5	$139.98	7.315%	$150.2195	$150.22	$150.20	$150.20
Purchase #6	$48.67	13.144%	$55.0672	$55.07	$55.05	$55.10
Purchase #7	$129.72	12.400%	$145.8053	$145.81	$145.80	$145.80
7 purchase totals =	$978.55		$1,089.8345	$1,089.84	$1,089.75	$1,089.80