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	$31.99	13.332%	$36.2549	$36.25	$36.25	$36.30
Purchase #2	$239.42	13.136%	$270.8702	$270.87	$270.85	$270.90
Purchase #3	$172.70	7.462%	$185.5869	$185.59	$185.60	$185.60
Purchase #4	$180.49	8.771%	$196.3208	$196.32	$196.30	$196.30
Purchase #5	$19.37	3.595%	$20.0664	$20.07	$20.05	$20.10
Purchase #6	$56.84	10.658%	$62.898	$62.90	$62.90	$62.90
Purchase #7	$85.71	3.340%	$88.5727	$88.57	$88.55	$88.60
7 purchase totals =	$786.52		$860.5699	$860.57	$860.50	$860.70