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	$138.54	6.394%	$147.3982	$147.40	$147.40	$147.40
Purchase #2	$151.64	5.531%	$160.0272	$160.03	$160.05	$160.00
Purchase #3	$250.37	13.708%	$284.6907	$284.69	$284.70	$284.70
Purchase #4	$10.50	9.544%	$11.5021	$11.50	$11.50	$11.50
Purchase #5	$156.41	5.306%	$164.7091	$164.71	$164.70	$164.70
Purchase #6	$72.86	7.142%	$78.0637	$78.06	$78.05	$78.10
Purchase #7	$68.32	6.568%	$72.8073	$72.81	$72.80	$72.80
7 purchase totals =	$848.64		$919.1983	$919.20	$919.20	$919.20