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	$204.72	12.230%	$229.7573	$229.76	$229.75	$229.80
Purchase #2	$74.83	4.781%	$78.4076	$78.41	$78.40	$78.40
Purchase #3	$19.28	12.677%	$21.7241	$21.72	$21.70	$21.70
Purchase #4	$127.65	11.552%	$142.3961	$142.40	$142.40	$142.40
Purchase #5	$246.39	6.268%	$261.8337	$261.83	$261.85	$261.80
Purchase #6	$93.73	6.124%	$99.47	$99.47	$99.45	$99.50
Purchase #7	$164.48	7.209%	$176.3374	$176.34	$176.35	$176.30
7 purchase totals =	$931.08		$1,009.9262	$1,009.93	$1,009.90	$1,009.90