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	$157.34	4.273%	$164.0631	$164.06	$164.05	$164.10
Purchase #2	$111.44	8.163%	$120.5368	$120.54	$120.55	$120.50
Purchase #3	$151.38	10.612%	$167.4444	$167.44	$167.45	$167.40
Purchase #4	$213.85	10.291%	$235.8573	$235.86	$235.85	$235.90
Purchase #5	$31.39	12.777%	$35.4007	$35.40	$35.40	$35.40
Purchase #6	$169.80	7.459%	$182.4654	$182.47	$182.45	$182.50
Purchase #7	$57.86	6.871%	$61.8356	$61.84	$61.85	$61.80
7 purchase totals =	$893.06		$967.6033	$967.61	$967.60	$967.60