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	$241.50	13.193%	$273.3611	$273.36	$273.35	$273.40
Purchase #2	$240.45	8.666%	$261.2874	$261.29	$261.30	$261.30
Purchase #3	$51.71	8.311%	$56.0076	$56.01	$56.00	$56.00
Purchase #4	$73.38	11.565%	$81.8664	$81.87	$81.85	$81.90
Purchase #5	$85.67	4.570%	$89.5851	$89.59	$89.60	$89.60
Purchase #6	$5.91	6.144%	$6.2731	$6.27	$6.25	$6.30
Purchase #7	$104.82	6.419%	$111.5484	$111.55	$111.55	$111.50
7 purchase totals =	$803.44		$879.9291	$879.94	$879.90	$880.00