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	$155.56	10.131%	$171.3198	$171.32	$171.30	$171.30
Purchase #2	$222.91	10.283%	$245.8318	$245.83	$245.85	$245.80
Purchase #3	$82.35	9.284%	$89.9954	$90.00	$90.00	$90.00
Purchase #4	$151.46	5.789%	$160.228	$160.23	$160.25	$160.20
Purchase #5	$200.33	4.184%	$208.7118	$208.71	$208.70	$208.70
Purchase #6	$19.46	9.331%	$21.2758	$21.28	$21.30	$21.30
Purchase #7	$126.67	13.238%	$143.4386	$143.44	$143.45	$143.40
7 purchase totals =	$958.74		$1,040.8012	$1,040.81	$1,040.85	$1,040.70