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	$123.90	11.180%	$137.752	$137.75	$137.75	$137.80
Purchase #2	$229.86	11.105%	$255.386	$255.39	$255.40	$255.40
Purchase #3	$59.40	4.404%	$62.016	$62.02	$62.00	$62.00
Purchase #4	$156.61	12.225%	$175.7556	$175.76	$175.75	$175.80
Purchase #5	$32.61	4.152%	$33.964	$33.96	$33.95	$34.00
Purchase #6	$178.82	8.314%	$193.6871	$193.69	$193.70	$193.70
Purchase #7	$133.82	5.644%	$141.3728	$141.37	$141.35	$141.40
7 purchase totals =	$915.02		$999.9335	$999.94	$999.90	$1,000.10