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	$29.70	5.506%	$31.3353	$31.34	$31.35	$31.30
Purchase #2	$179.29	5.632%	$189.3876	$189.39	$189.40	$189.40
Purchase #3	$171.75	10.836%	$190.3608	$190.36	$190.35	$190.40
Purchase #4	$228.75	4.458%	$238.9477	$238.95	$238.95	$238.90
Purchase #5	$32.78	5.300%	$34.5173	$34.52	$34.50	$34.50
Purchase #6	$199.79	9.349%	$218.4684	$218.47	$218.45	$218.50
Purchase #7	$162.81	12.668%	$183.4348	$183.43	$183.45	$183.40
7 purchase totals =	$1,004.87		$1,086.4519	$1,086.46	$1,086.45	$1,086.40