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	$187.92	8.196%	$203.3219	$203.32	$203.30	$203.30
Purchase #2	$24.78	10.699%	$27.4312	$27.43	$27.45	$27.40
Purchase #3	$150.90	9.710%	$165.5524	$165.55	$165.55	$165.60
Purchase #4	$11.86	12.297%	$13.3184	$13.32	$13.30	$13.30
Purchase #5	$42.57	6.627%	$45.3911	$45.39	$45.40	$45.40
Purchase #6	$100.71	12.691%	$113.4911	$113.49	$113.50	$113.50
Purchase #7	$46.98	9.322%	$51.3595	$51.36	$51.35	$51.40
7 purchase totals =	$565.72		$619.8656	$619.86	$619.85	$619.90