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	$227.83	5.128%	$239.5131	$239.51	$239.50	$239.50
Purchase #2	$174.31	8.285%	$188.7516	$188.75	$188.75	$188.80
Purchase #3	$137.97	9.116%	$150.5473	$150.55	$150.55	$150.50
Purchase #4	$85.46	12.616%	$96.2416	$96.24	$96.25	$96.20
Purchase #5	$51.86	9.241%	$56.6524	$56.65	$56.65	$56.70
Purchase #6	$11.33	13.566%	$12.867	$12.87	$12.85	$12.90
Purchase #7	$37.58	6.476%	$40.0137	$40.01	$40.00	$40.00
7 purchase totals =	$726.34		$784.5867	$784.58	$784.55	$784.60