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	$117.27	9.343%	$128.2265	$128.23	$128.25	$128.20
Purchase #2	$188.89	6.321%	$200.8297	$200.83	$200.85	$200.80
Purchase #3	$123.56	10.664%	$136.7364	$136.74	$136.75	$136.70
Purchase #4	$43.83	9.321%	$47.9154	$47.92	$47.90	$47.90
Purchase #5	$91.94	9.468%	$100.6449	$100.64	$100.65	$100.60
Purchase #6	$93.43	11.714%	$104.3744	$104.37	$104.35	$104.40
Purchase #7	$124.50	10.554%	$137.6397	$137.64	$137.65	$137.60
7 purchase totals =	$783.42		$856.3670	$856.37	$856.40	$856.20