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	$169.88	12.443%	$191.0182	$191.02	$191.00	$191.00
Purchase #2	$37.97	6.207%	$40.3268	$40.33	$40.35	$40.30
Purchase #3	$237.51	3.670%	$246.2266	$246.23	$246.25	$246.20
Purchase #4	$181.76	9.242%	$198.5583	$198.56	$198.55	$198.60
Purchase #5	$50.35	5.709%	$53.2245	$53.22	$53.20	$53.20
Purchase #6	$141.59	13.616%	$160.8689	$160.87	$160.85	$160.90
Purchase #7	$51.32	10.429%	$56.6722	$56.67	$56.65	$56.70
7 purchase totals =	$870.38		$946.8955	$946.90	$946.85	$946.90