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	$161.58	6.725%	$172.4463	$172.45	$172.45	$172.40
Purchase #2	$155.63	10.308%	$171.6723	$171.67	$171.65	$171.70
Purchase #3	$196.56	9.749%	$215.7226	$215.72	$215.70	$215.70
Purchase #4	$29.48	5.660%	$31.1486	$31.15	$31.15	$31.10
Purchase #5	$230.94	4.425%	$241.1591	$241.16	$241.15	$241.20
Purchase #6	$195.54	7.354%	$209.92	$209.92	$209.90	$209.90
Purchase #7	$172.29	10.181%	$189.8308	$189.83	$189.85	$189.80
7 purchase totals =	$1,142.02		$1,231.8997	$1,231.90	$1,231.85	$1,231.80