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	$137.44	3.503%	$142.2545	$142.25	$142.25	$142.30
Purchase #2	$93.87	10.655%	$103.8718	$103.87	$103.85	$103.90
Purchase #3	$90.97	9.848%	$99.9287	$99.93	$99.95	$99.90
Purchase #4	$120.67	9.307%	$131.9008	$131.90	$131.90	$131.90
Purchase #5	$20.76	3.519%	$21.4905	$21.49	$21.50	$21.50
Purchase #6	$107.59	9.351%	$117.6507	$117.65	$117.65	$117.70
Purchase #7	$59.77	8.279%	$64.7184	$64.72	$64.70	$64.70
7 purchase totals =	$631.07		$681.8154	$681.81	$681.80	$681.90