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	$154.41	6.691%	$164.7416	$164.74	$164.75	$164.70
Purchase #2	$141.56	13.426%	$160.5658	$160.57	$160.55	$160.60
Purchase #3	$130.45	4.524%	$136.3516	$136.35	$136.35	$136.40
Purchase #4	$210.56	8.418%	$228.2849	$228.28	$228.30	$228.30
Purchase #5	$103.56	5.622%	$109.3821	$109.38	$109.40	$109.40
Purchase #6	$233.89	11.616%	$261.0587	$261.06	$261.05	$261.10
Purchase #7	$46.74	10.326%	$51.5664	$51.57	$51.55	$51.60
7 purchase totals =	$1,021.17		$1,111.9511	$1,111.95	$1,111.95	$1,112.10