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	$201.83	13.207%	$228.4857	$228.49	$228.50	$228.50
Purchase #2	$146.90	10.792%	$162.7534	$162.75	$162.75	$162.80
Purchase #3	$155.33	9.770%	$170.5057	$170.51	$170.50	$170.50
Purchase #4	$186.35	6.725%	$198.882	$198.88	$198.90	$198.90
Purchase #5	$222.89	12.743%	$251.2929	$251.29	$251.30	$251.30
Purchase #6	$85.77	4.757%	$89.8501	$89.85	$89.85	$89.90
Purchase #7	$167.25	12.373%	$187.9438	$187.94	$187.95	$187.90
7 purchase totals =	$1,166.32		$1,289.7136	$1,289.71	$1,289.75	$1,289.80