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	$123.31	13.448%	$139.8927	$139.89	$139.90	$139.90
Purchase #2	$175.39	4.263%	$182.8669	$182.87	$182.85	$182.90
Purchase #3	$118.32	3.252%	$122.1678	$122.17	$122.15	$122.20
Purchase #4	$249.94	12.244%	$280.5427	$280.54	$280.55	$280.50
Purchase #5	$148.47	10.638%	$164.2642	$164.26	$164.25	$164.30
Purchase #6	$142.94	13.468%	$162.1912	$162.19	$162.20	$162.20
Purchase #7	$209.36	5.584%	$221.0507	$221.05	$221.05	$221.10
7 purchase totals =	$1,167.73		$1,272.9762	$1,272.97	$1,272.95	$1,273.10