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	$228.49	9.706%	$250.6672	$250.67	$250.65	$250.70
Purchase #2	$200.71	10.750%	$222.2863	$222.29	$222.30	$222.30
Purchase #3	$125.92	11.478%	$140.3731	$140.37	$140.35	$140.40
Purchase #4	$17.65	9.583%	$19.3414	$19.34	$19.35	$19.30
Purchase #5	$198.75	7.844%	$214.34	$214.34	$214.35	$214.30
Purchase #6	$219.44	6.348%	$233.3701	$233.37	$233.35	$233.40
Purchase #7	$18.36	11.497%	$20.4708	$20.47	$20.45	$20.50
7 purchase totals =	$1,009.32		$1,100.8489	$1,100.85	$1,100.80	$1,100.90