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	$19.80	12.697%	$22.314	$22.31	$22.30	$22.30
Purchase #2	$183.40	4.398%	$191.4659	$191.47	$191.45	$191.50
Purchase #3	$24.37	11.386%	$27.1448	$27.14	$27.15	$27.10
Purchase #4	$71.32	12.659%	$80.3484	$80.35	$80.35	$80.30
Purchase #5	$103.70	9.508%	$113.5598	$113.56	$113.55	$113.60
Purchase #6	$12.72	11.398%	$14.1698	$14.17	$14.15	$14.20
Purchase #7	$201.49	7.650%	$216.904	$216.90	$216.90	$216.90
7 purchase totals =	$616.80		$665.9067	$665.90	$665.85	$665.90