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	$82.32	9.644%	$90.2589	$90.26	$90.25	$90.30
Purchase #2	$182.82	3.642%	$189.4783	$189.48	$189.50	$189.50
Purchase #3	$122.32	12.352%	$137.429	$137.43	$137.45	$137.40
Purchase #4	$172.67	11.340%	$192.2508	$192.25	$192.25	$192.30
Purchase #5	$242.71	5.279%	$255.5227	$255.52	$255.50	$255.50
Purchase #6	$234.25	4.660%	$245.1661	$245.17	$245.15	$245.20
Purchase #7	$46.35	10.595%	$51.2608	$51.26	$51.25	$51.30
7 purchase totals =	$1,083.44		$1,161.3666	$1,161.37	$1,161.35	$1,161.50