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	$207.81	4.205%	$216.5484	$216.55	$216.55	$216.50
Purchase #2	$162.68	13.743%	$185.0371	$185.04	$185.05	$185.00
Purchase #3	$167.63	12.862%	$189.1906	$189.19	$189.20	$189.20
Purchase #4	$85.43	4.500%	$89.2744	$89.27	$89.25	$89.30
Purchase #5	$37.50	5.243%	$39.4661	$39.47	$39.45	$39.50
Purchase #6	$108.94	6.327%	$115.8326	$115.83	$115.85	$115.80
Purchase #7	$78.99	5.711%	$83.5011	$83.50	$83.50	$83.50
7 purchase totals =	$848.98		$918.8503	$918.85	$918.85	$918.80