Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$135.83	8.820%	$147.8102	$147.81	$147.80	$147.80
Purchase #2	$222.39	6.871%	$237.6704	$237.67	$237.65	$237.70
Purchase #3	$13.35	5.316%	$14.0597	$14.06	$14.05	$14.10
Purchase #4	$175.64	11.776%	$196.3234	$196.32	$196.30	$196.30
Purchase #5	$117.48	3.458%	$121.5425	$121.54	$121.55	$121.50
Purchase #6	$41.86	9.158%	$45.6935	$45.69	$45.70	$45.70
Purchase #7	$186.34	5.524%	$196.6334	$196.63	$196.65	$196.60
7 purchase totals =	$892.89		$959.7331	$959.72	$959.70	$959.70