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	$240.32	3.760%	$249.356	$249.36	$249.35	$249.40
Purchase #2	$173.74	12.845%	$196.0569	$196.06	$196.05	$196.10
Purchase #3	$69.52	12.400%	$78.1405	$78.14	$78.15	$78.10
Purchase #4	$113.32	8.796%	$123.2876	$123.29	$123.30	$123.30
Purchase #5	$199.56	8.600%	$216.7222	$216.72	$216.70	$216.70
Purchase #6	$124.68	11.509%	$139.0294	$139.03	$139.05	$139.00
Purchase #7	$244.46	4.821%	$256.2454	$256.25	$256.25	$256.20
7 purchase totals =	$1,165.60		$1,258.8380	$1,258.85	$1,258.85	$1,258.80