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	$241.98	5.728%	$255.8406	$255.84	$255.85	$255.80
Purchase #2	$50.98	12.703%	$57.456	$57.46	$57.45	$57.50
Purchase #3	$211.43	5.747%	$223.5809	$223.58	$223.60	$223.60
Purchase #4	$141.41	12.339%	$158.8586	$158.86	$158.85	$158.90
Purchase #5	$32.48	3.323%	$33.5593	$33.56	$33.55	$33.60
Purchase #6	$141.65	3.575%	$146.714	$146.71	$146.70	$146.70
Purchase #7	$201.45	4.849%	$211.2183	$211.22	$211.20	$211.20
7 purchase totals =	$1,021.38		$1,087.2277	$1,087.23	$1,087.20	$1,087.30