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	$90.60	10.718%	$100.3105	$100.31	$100.30	$100.30
Purchase #2	$208.91	6.573%	$222.6417	$222.64	$222.65	$222.60
Purchase #3	$87.81	8.487%	$95.2624	$95.26	$95.25	$95.30
Purchase #4	$28.96	10.135%	$31.8951	$31.90	$31.90	$31.90
Purchase #5	$143.26	3.304%	$147.9933	$147.99	$148.00	$148.00
Purchase #6	$213.40	9.484%	$233.6389	$233.64	$233.65	$233.60
Purchase #7	$150.25	5.199%	$158.0615	$158.06	$158.05	$158.10
7 purchase totals =	$923.19		$989.8034	$989.80	$989.80	$989.80