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	$83.45	8.240%	$90.3263	$90.33	$90.35	$90.30
Purchase #2	$199.59	5.294%	$210.1563	$210.16	$210.15	$210.20
Purchase #3	$72.92	12.638%	$82.1356	$82.14	$82.15	$82.10
Purchase #4	$144.27	7.796%	$155.5173	$155.52	$155.50	$155.50
Purchase #5	$231.68	10.646%	$256.3447	$256.34	$256.35	$256.30
Purchase #6	$187.79	6.153%	$199.3447	$199.34	$199.35	$199.30
Purchase #7	$143.29	8.622%	$155.6445	$155.64	$155.65	$155.60
7 purchase totals =	$1,062.99		$1,149.4694	$1,149.47	$1,149.50	$1,149.30