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	$36.41	6.118%	$38.6376	$38.64	$38.65	$38.60
Purchase #2	$163.59	11.616%	$182.5926	$182.59	$182.60	$182.60
Purchase #3	$38.86	11.785%	$43.4397	$43.44	$43.45	$43.40
Purchase #4	$83.35	11.644%	$93.0553	$93.06	$93.05	$93.10
Purchase #5	$167.84	11.304%	$186.8126	$186.81	$186.80	$186.80
Purchase #6	$44.74	9.113%	$48.8172	$48.82	$48.80	$48.80
Purchase #7	$71.30	3.545%	$73.8276	$73.83	$73.85	$73.80
7 purchase totals =	$606.09		$667.1826	$667.19	$667.20	$667.10