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	$40.61	6.857%	$43.3946	$43.39	$43.40	$43.40
Purchase #2	$110.44	13.673%	$125.5405	$125.54	$125.55	$125.50
Purchase #3	$142.88	5.792%	$151.1556	$151.16	$151.15	$151.20
Purchase #4	$225.31	8.228%	$243.8485	$243.85	$243.85	$243.80
Purchase #5	$85.83	5.509%	$90.5584	$90.56	$90.55	$90.60
Purchase #6	$42.94	13.830%	$48.8786	$48.88	$48.90	$48.90
Purchase #7	$99.25	7.824%	$107.0153	$107.02	$107.00	$107.00
7 purchase totals =	$747.26		$810.3915	$810.40	$810.40	$810.40