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	$78.43	7.111%	$84.0072	$84.01	$84.00	$84.00
Purchase #2	$43.29	4.805%	$45.3701	$45.37	$45.35	$45.40
Purchase #3	$40.90	12.183%	$45.8828	$45.88	$45.90	$45.90
Purchase #4	$68.81	9.460%	$75.3194	$75.32	$75.30	$75.30
Purchase #5	$45.35	3.246%	$46.8221	$46.82	$46.80	$46.80
Purchase #6	$228.83	10.722%	$253.3652	$253.37	$253.35	$253.40
Purchase #7	$90.38	10.470%	$99.8428	$99.84	$99.85	$99.80
7 purchase totals =	$595.99		$650.6096	$650.61	$650.55	$650.60