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	$220.75	9.823%	$242.4343	$242.43	$242.45	$242.40
Purchase #2	$170.72	7.328%	$183.2304	$183.23	$183.25	$183.20
Purchase #3	$213.47	13.128%	$241.4943	$241.49	$241.50	$241.50
Purchase #4	$112.66	3.538%	$116.6459	$116.65	$116.65	$116.60
Purchase #5	$39.35	13.681%	$44.7335	$44.73	$44.75	$44.70
Purchase #6	$91.90	9.409%	$100.5469	$100.55	$100.55	$100.50
Purchase #7	$101.67	9.340%	$111.166	$111.17	$111.15	$111.20
7 purchase totals =	$950.52		$1,040.2513	$1,040.25	$1,040.30	$1,040.10