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	$48.65	13.754%	$55.3413	$55.34	$55.35	$55.30
Purchase #2	$100.54	4.363%	$104.9266	$104.93	$104.95	$104.90
Purchase #3	$197.74	3.417%	$204.4968	$204.50	$204.50	$204.50
Purchase #4	$29.31	13.525%	$33.2742	$33.27	$33.25	$33.30
Purchase #5	$203.55	9.841%	$223.5814	$223.58	$223.60	$223.60
Purchase #6	$167.48	10.651%	$185.3183	$185.32	$185.30	$185.30
Purchase #7	$211.65	9.144%	$231.0033	$231.00	$231.00	$231.00
7 purchase totals =	$958.92		$1,037.9419	$1,037.94	$1,037.95	$1,037.90