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	$206.53	10.638%	$228.5007	$228.50	$228.50	$228.50
Purchase #2	$20.75	5.224%	$21.834	$21.83	$21.85	$21.80
Purchase #3	$152.90	12.432%	$171.9085	$171.91	$171.90	$171.90
Purchase #4	$223.53	6.603%	$238.2897	$238.29	$238.30	$238.30
Purchase #5	$115.35	9.244%	$126.013	$126.01	$126.00	$126.00
Purchase #6	$38.32	10.129%	$42.2014	$42.20	$42.20	$42.20
Purchase #7	$43.96	10.223%	$48.454	$48.45	$48.45	$48.50
7 purchase totals =	$801.34		$877.2013	$877.19	$877.20	$877.20