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	$10.94	3.511%	$11.3241	$11.32	$11.30	$11.30
Purchase #2	$141.53	12.205%	$158.8037	$158.80	$158.80	$158.80
Purchase #3	$195.34	8.487%	$211.9185	$211.92	$211.90	$211.90
Purchase #4	$130.70	10.273%	$144.1268	$144.13	$144.15	$144.10
Purchase #5	$211.89	9.170%	$231.3203	$231.32	$231.30	$231.30
Purchase #6	$103.31	12.616%	$116.3436	$116.34	$116.35	$116.30
Purchase #7	$221.35	9.474%	$242.3207	$242.32	$242.30	$242.30
7 purchase totals =	$1,015.06		$1,116.1577	$1,116.15	$1,116.10	$1,116.00