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	$71.97	9.402%	$78.7366	$78.74	$78.75	$78.70
Purchase #2	$144.86	12.417%	$162.8473	$162.85	$162.85	$162.80
Purchase #3	$85.28	4.587%	$89.1918	$89.19	$89.20	$89.20
Purchase #4	$90.29	13.249%	$102.2525	$102.25	$102.25	$102.30
Purchase #5	$120.45	13.653%	$136.895	$136.90	$136.90	$136.90
Purchase #6	$60.78	12.426%	$68.3325	$68.33	$68.35	$68.30
Purchase #7	$43.60	4.597%	$45.6043	$45.60	$45.60	$45.60
7 purchase totals =	$617.23		$683.8600	$683.86	$683.90	$683.80