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	$222.36	8.286%	$240.7847	$240.78	$240.80	$240.80
Purchase #2	$94.79	7.209%	$101.6234	$101.62	$101.60	$101.60
Purchase #3	$67.92	7.123%	$72.7579	$72.76	$72.75	$72.80
Purchase #4	$24.64	13.164%	$27.8836	$27.88	$27.90	$27.90
Purchase #5	$199.47	7.199%	$213.8298	$213.83	$213.85	$213.80
Purchase #6	$68.35	4.533%	$71.4483	$71.45	$71.45	$71.40
Purchase #7	$78.92	11.487%	$87.9855	$87.99	$88.00	$88.00
7 purchase totals =	$756.45		$816.3132	$816.31	$816.35	$816.30