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	$131.60	6.699%	$140.4159	$140.42	$140.40	$140.40
Purchase #2	$43.54	8.161%	$47.0933	$47.09	$47.10	$47.10
Purchase #3	$250.50	13.829%	$285.1416	$285.14	$285.15	$285.10
Purchase #4	$27.90	13.864%	$31.7681	$31.77	$31.75	$31.80
Purchase #5	$202.71	5.349%	$213.553	$213.55	$213.55	$213.60
Purchase #6	$111.53	10.299%	$123.0165	$123.02	$123.00	$123.00
Purchase #7	$245.40	5.740%	$259.486	$259.49	$259.50	$259.50
7 purchase totals =	$1,013.18		$1,100.4744	$1,100.48	$1,100.45	$1,100.50