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	$179.80	5.596%	$189.8616	$189.86	$189.85	$189.90
Purchase #2	$89.30	3.289%	$92.2371	$92.24	$92.25	$92.20
Purchase #3	$34.47	11.610%	$38.472	$38.47	$38.45	$38.50
Purchase #4	$161.32	4.473%	$168.5358	$168.54	$168.55	$168.50
Purchase #5	$213.89	10.709%	$236.7955	$236.80	$236.80	$236.80
Purchase #6	$65.30	11.541%	$72.8363	$72.84	$72.85	$72.80
Purchase #7	$161.52	3.431%	$167.0618	$167.06	$167.05	$167.10
7 purchase totals =	$905.60		$965.8001	$965.81	$965.80	$965.80