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	$73.82	6.870%	$78.8914	$78.89	$78.90	$78.90
Purchase #2	$138.32	7.599%	$148.8309	$148.83	$148.85	$148.80
Purchase #3	$100.42	13.740%	$114.2177	$114.22	$114.20	$114.20
Purchase #4	$91.79	5.365%	$96.7145	$96.71	$96.70	$96.70
Purchase #5	$137.71	5.627%	$145.4589	$145.46	$145.45	$145.50
Purchase #6	$59.63	10.409%	$65.8369	$65.84	$65.85	$65.80
Purchase #7	$214.90	8.245%	$232.6185	$232.62	$232.60	$232.60
7 purchase totals =	$816.59		$882.5688	$882.57	$882.55	$882.50