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	$129.93	5.854%	$137.5361	$137.54	$137.55	$137.50
Purchase #2	$116.51	6.748%	$124.3721	$124.37	$124.35	$124.40
Purchase #3	$213.93	11.412%	$238.3437	$238.34	$238.35	$238.30
Purchase #4	$39.37	11.236%	$43.7936	$43.79	$43.80	$43.80
Purchase #5	$74.61	12.109%	$83.6445	$83.64	$83.65	$83.60
Purchase #6	$89.54	4.810%	$93.8469	$93.85	$93.85	$93.80
Purchase #7	$150.67	11.192%	$167.533	$167.53	$167.55	$167.50
7 purchase totals =	$814.56		$889.0699	$889.06	$889.10	$888.90