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	$99.63	3.590%	$103.2067	$103.21	$103.20	$103.20
Purchase #2	$97.74	8.340%	$105.8915	$105.89	$105.90	$105.90
Purchase #3	$222.92	8.827%	$242.5971	$242.60	$242.60	$242.60
Purchase #4	$41.25	3.801%	$42.8179	$42.82	$42.80	$42.80
Purchase #5	$162.40	12.106%	$182.0601	$182.06	$182.05	$182.10
Purchase #6	$228.30	5.193%	$240.1556	$240.16	$240.15	$240.20
Purchase #7	$163.26	11.157%	$181.4749	$181.47	$181.45	$181.50
7 purchase totals =	$1,015.50		$1,098.2038	$1,098.21	$1,098.15	$1,098.30