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	$45.96	11.831%	$51.3975	$51.40	$51.40	$51.40
Purchase #2	$96.71	13.141%	$109.4187	$109.42	$109.40	$109.40
Purchase #3	$117.90	4.227%	$122.8836	$122.88	$122.90	$122.90
Purchase #4	$220.47	8.354%	$238.8881	$238.89	$238.90	$238.90
Purchase #5	$231.75	12.215%	$260.0583	$260.06	$260.05	$260.10
Purchase #6	$43.59	6.294%	$46.3336	$46.33	$46.35	$46.30
Purchase #7	$201.90	10.864%	$223.8344	$223.83	$223.85	$223.80
7 purchase totals =	$958.28		$1,052.8142	$1,052.81	$1,052.85	$1,052.80