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	$111.72	9.128%	$121.9178	$121.92	$121.90	$121.90
Purchase #2	$104.47	6.812%	$111.5865	$111.59	$111.60	$111.60
Purchase #3	$191.65	8.462%	$207.8674	$207.87	$207.85	$207.90
Purchase #4	$97.29	12.430%	$109.3831	$109.38	$109.40	$109.40
Purchase #5	$163.61	13.721%	$186.0589	$186.06	$186.05	$186.10
Purchase #6	$31.88	4.415%	$33.2875	$33.29	$33.30	$33.30
Purchase #7	$146.79	6.516%	$156.3548	$156.35	$156.35	$156.40
7 purchase totals =	$847.41		$926.4560	$926.46	$926.45	$926.60