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	$82.68	9.276%	$90.3494	$90.35	$90.35	$90.30
Purchase #2	$82.90	9.284%	$90.5964	$90.60	$90.60	$90.60
Purchase #3	$85.46	10.637%	$94.5504	$94.55	$94.55	$94.60
Purchase #4	$36.60	9.481%	$40.07	$40.07	$40.05	$40.10
Purchase #5	$197.59	5.104%	$207.675	$207.68	$207.70	$207.70
Purchase #6	$142.58	4.349%	$148.7808	$148.78	$148.80	$148.80
Purchase #7	$228.62	7.243%	$245.1789	$245.18	$245.20	$245.20
7 purchase totals =	$856.43		$917.2009	$917.21	$917.25	$917.30