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	$17.85	4.245%	$18.6077	$18.61	$18.60	$18.60
Purchase #2	$97.78	7.527%	$105.1399	$105.14	$105.15	$105.10
Purchase #3	$92.90	5.808%	$98.2956	$98.30	$98.30	$98.30
Purchase #4	$87.81	13.750%	$99.8839	$99.88	$99.90	$99.90
Purchase #5	$250.95	6.127%	$266.3257	$266.33	$266.35	$266.30
Purchase #6	$131.52	9.601%	$144.1472	$144.15	$144.15	$144.10
Purchase #7	$141.78	3.823%	$147.2002	$147.20	$147.20	$147.20
7 purchase totals =	$820.59		$879.6002	$879.61	$879.65	$879.50