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	$133.72	13.337%	$151.5542	$151.55	$151.55	$151.60
Purchase #2	$122.44	5.206%	$128.8142	$128.81	$128.80	$128.80
Purchase #3	$67.67	7.248%	$72.5747	$72.57	$72.55	$72.60
Purchase #4	$82.45	8.539%	$89.4904	$89.49	$89.50	$89.50
Purchase #5	$189.49	9.363%	$207.2319	$207.23	$207.25	$207.20
Purchase #6	$155.77	7.766%	$167.8671	$167.87	$167.85	$167.90
Purchase #7	$36.40	8.714%	$39.5719	$39.57	$39.55	$39.60
7 purchase totals =	$787.94		$857.1044	$857.09	$857.05	$857.20