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	$150.58	11.296%	$167.5895	$167.59	$167.60	$167.60
Purchase #2	$247.37	13.557%	$280.906	$280.91	$280.90	$280.90
Purchase #3	$143.45	9.135%	$156.5542	$156.55	$156.55	$156.60
Purchase #4	$237.66	13.841%	$270.5545	$270.55	$270.55	$270.60
Purchase #5	$183.71	11.534%	$204.8991	$204.90	$204.90	$204.90
Purchase #6	$125.27	11.503%	$139.6798	$139.68	$139.70	$139.70
Purchase #7	$72.38	12.558%	$81.4695	$81.47	$81.45	$81.50
7 purchase totals =	$1,160.42		$1,301.6526	$1,301.65	$1,301.65	$1,301.80