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	$163.67	5.420%	$172.5409	$172.54	$172.55	$172.50
Purchase #2	$200.85	11.539%	$224.0261	$224.03	$224.05	$224.00
Purchase #3	$86.55	10.210%	$95.3868	$95.39	$95.40	$95.40
Purchase #4	$80.97	6.554%	$86.2768	$86.28	$86.30	$86.30
Purchase #5	$93.78	10.294%	$103.4337	$103.43	$103.45	$103.40
Purchase #6	$131.34	10.689%	$145.3789	$145.38	$145.40	$145.40
Purchase #7	$29.30	5.503%	$30.9124	$30.91	$30.90	$30.90
7 purchase totals =	$786.46		$857.9556	$857.96	$858.05	$857.90