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	$178.89	13.638%	$203.287	$203.29	$203.30	$203.30
Purchase #2	$178.93	9.808%	$196.4795	$196.48	$196.50	$196.50
Purchase #3	$84.86	6.419%	$90.3072	$90.31	$90.30	$90.30
Purchase #4	$237.34	4.390%	$247.7592	$247.76	$247.75	$247.80
Purchase #5	$48.73	6.304%	$51.8019	$51.80	$51.80	$51.80
Purchase #6	$75.71	6.441%	$80.5865	$80.59	$80.60	$80.60
Purchase #7	$153.80	6.792%	$164.2461	$164.25	$164.25	$164.20
7 purchase totals =	$958.26		$1,034.4674	$1,034.48	$1,034.50	$1,034.50