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	$250.77	4.685%	$262.5186	$262.52	$262.50	$262.50
Purchase #2	$150.46	13.665%	$171.0204	$171.02	$171.00	$171.00
Purchase #3	$174.30	13.319%	$197.515	$197.52	$197.50	$197.50
Purchase #4	$98.70	5.113%	$103.7465	$103.75	$103.75	$103.70
Purchase #5	$236.75	10.439%	$261.4643	$261.46	$261.45	$261.50
Purchase #6	$171.25	8.352%	$185.5528	$185.55	$185.55	$185.60
Purchase #7	$186.83	13.419%	$211.9007	$211.90	$211.90	$211.90
7 purchase totals =	$1,269.06		$1,393.7183	$1,393.72	$1,393.65	$1,393.70