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	$85.76	4.187%	$89.3508	$89.35	$89.35	$89.40
Purchase #2	$154.84	9.824%	$170.0515	$170.05	$170.05	$170.10
Purchase #3	$198.96	13.137%	$225.0974	$225.10	$225.10	$225.10
Purchase #4	$206.50	8.198%	$223.4289	$223.43	$223.45	$223.40
Purchase #5	$220.33	13.257%	$249.5391	$249.54	$249.55	$249.50
Purchase #6	$103.59	9.369%	$113.2953	$113.30	$113.30	$113.30
Purchase #7	$217.27	11.189%	$241.5803	$241.58	$241.60	$241.60
7 purchase totals =	$1,187.25		$1,312.3433	$1,312.35	$1,312.40	$1,312.40