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	$186.25	12.245%	$209.0563	$209.06	$209.05	$209.10
Purchase #2	$215.45	11.848%	$240.9765	$240.98	$241.00	$241.00
Purchase #3	$64.89	7.273%	$69.6094	$69.61	$69.60	$69.60
Purchase #4	$77.53	11.721%	$86.6173	$86.62	$86.60	$86.60
Purchase #5	$96.49	13.575%	$109.5885	$109.59	$109.60	$109.60
Purchase #6	$69.48	5.509%	$73.3077	$73.31	$73.30	$73.30
Purchase #7	$50.28	8.830%	$54.7197	$54.72	$54.70	$54.70
7 purchase totals =	$760.37		$843.8754	$843.89	$843.85	$843.90