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	$226.35	6.368%	$240.764	$240.76	$240.75	$240.80
Purchase #2	$126.83	7.737%	$136.6428	$136.64	$136.65	$136.60
Purchase #3	$155.48	5.824%	$164.5352	$164.54	$164.55	$164.50
Purchase #4	$64.27	11.611%	$71.7324	$71.73	$71.75	$71.70
Purchase #5	$136.61	12.374%	$153.5141	$153.51	$153.50	$153.50
Purchase #6	$64.25	9.686%	$70.4733	$70.47	$70.45	$70.50
Purchase #7	$227.82	8.601%	$247.4148	$247.41	$247.40	$247.40
7 purchase totals =	$1,001.61		$1,085.0766	$1,085.06	$1,085.05	$1,085.00