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	$123.58	6.573%	$131.7029	$131.70	$131.70	$131.70
Purchase #2	$154.46	11.653%	$172.4592	$172.46	$172.45	$172.50
Purchase #3	$160.56	8.553%	$174.2927	$174.29	$174.30	$174.30
Purchase #4	$102.77	5.398%	$108.3175	$108.32	$108.30	$108.30
Purchase #5	$96.67	3.701%	$100.2478	$100.25	$100.25	$100.20
Purchase #6	$162.58	8.810%	$176.9033	$176.90	$176.90	$176.90
Purchase #7	$215.70	12.683%	$243.0572	$243.06	$243.05	$243.10
7 purchase totals =	$1,016.32		$1,106.9806	$1,106.98	$1,106.95	$1,107.00