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	$163.62	11.712%	$182.7832	$182.78	$182.80	$182.80
Purchase #2	$27.89	11.483%	$31.0926	$31.09	$31.10	$31.10
Purchase #3	$28.44	13.620%	$32.3135	$32.31	$32.30	$32.30
Purchase #4	$161.75	4.251%	$168.626	$168.63	$168.65	$168.60
Purchase #5	$52.83	8.657%	$57.4035	$57.40	$57.40	$57.40
Purchase #6	$76.66	11.470%	$85.4529	$85.45	$85.45	$85.50
Purchase #7	$77.38	5.120%	$81.3419	$81.34	$81.35	$81.30
7 purchase totals =	$588.57		$639.0136	$639.00	$639.05	$639.00