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	$249.50	13.835%	$284.0183	$284.02	$284.00	$284.00
Purchase #2	$173.45	5.286%	$182.6186	$182.62	$182.60	$182.60
Purchase #3	$86.81	9.260%	$94.8486	$94.85	$94.85	$94.80
Purchase #4	$165.90	6.619%	$176.8809	$176.88	$176.90	$176.90
Purchase #5	$164.83	12.772%	$185.8821	$185.88	$185.90	$185.90
Purchase #6	$181.43	8.433%	$196.73	$196.73	$196.75	$196.70
Purchase #7	$21.84	12.762%	$24.6272	$24.63	$24.65	$24.60
7 purchase totals =	$1,043.76		$1,145.6057	$1,145.61	$1,145.65	$1,145.50