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	$168.54	5.810%	$178.3322	$178.33	$178.35	$178.30
Purchase #2	$73.83	5.395%	$77.8131	$77.81	$77.80	$77.80
Purchase #3	$107.65	8.107%	$116.3772	$116.38	$116.40	$116.40
Purchase #4	$147.90	6.118%	$156.9485	$156.95	$156.95	$156.90
Purchase #5	$19.33	7.226%	$20.7268	$20.73	$20.75	$20.70
Purchase #6	$35.37	13.271%	$40.064	$40.06	$40.05	$40.10
Purchase #7	$63.42	6.589%	$67.5987	$67.60	$67.60	$67.60
7 purchase totals =	$616.04		$657.8605	$657.86	$657.90	$657.80