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	$155.50	8.376%	$168.5247	$168.52	$168.50	$168.50
Purchase #2	$135.76	4.243%	$141.5203	$141.52	$141.50	$141.50
Purchase #3	$199.75	9.379%	$218.4846	$218.48	$218.50	$218.50
Purchase #4	$67.77	12.837%	$76.4696	$76.47	$76.45	$76.50
Purchase #5	$42.41	9.645%	$46.5004	$46.50	$46.50	$46.50
Purchase #6	$81.49	11.125%	$90.5558	$90.56	$90.55	$90.60
Purchase #7	$13.94	9.605%	$15.2789	$15.28	$15.30	$15.30
7 purchase totals =	$696.62		$757.3343	$757.33	$757.30	$757.40