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	$30.52	7.609%	$32.8423	$32.84	$32.85	$32.80
Purchase #2	$10.26	11.352%	$11.4247	$11.42	$11.40	$11.40
Purchase #3	$167.81	13.542%	$190.5348	$190.53	$190.55	$190.50
Purchase #4	$182.61	11.820%	$204.1945	$204.19	$204.20	$204.20
Purchase #5	$202.30	12.506%	$227.5996	$227.60	$227.60	$227.60
Purchase #6	$157.72	6.700%	$168.2872	$168.29	$168.30	$168.30
Purchase #7	$127.76	11.754%	$142.7769	$142.78	$142.80	$142.80
7 purchase totals =	$878.98		$977.6600	$977.65	$977.70	$977.60