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	$250.86	13.635%	$285.0648	$285.06	$285.05	$285.10
Purchase #2	$45.86	11.653%	$51.2041	$51.20	$51.20	$51.20
Purchase #3	$100.51	4.177%	$104.7083	$104.71	$104.70	$104.70
Purchase #4	$178.96	12.214%	$200.8182	$200.82	$200.80	$200.80
Purchase #5	$148.73	6.448%	$158.3201	$158.32	$158.30	$158.30
Purchase #6	$25.25	7.807%	$27.2213	$27.22	$27.20	$27.20
Purchase #7	$96.91	7.858%	$104.5252	$104.53	$104.55	$104.50
7 purchase totals =	$847.08		$931.8620	$931.86	$931.80	$931.80