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	$67.84	6.312%	$72.1221	$72.12	$72.10	$72.10
Purchase #2	$64.34	4.370%	$67.1517	$67.15	$67.15	$67.20
Purchase #3	$217.79	4.344%	$227.2508	$227.25	$227.25	$227.30
Purchase #4	$146.60	12.401%	$164.7799	$164.78	$164.80	$164.80
Purchase #5	$104.84	11.457%	$116.8515	$116.85	$116.85	$116.90
Purchase #6	$120.97	8.588%	$131.3589	$131.36	$131.35	$131.40
Purchase #7	$92.25	10.603%	$102.0313	$102.03	$102.05	$102.00
7 purchase totals =	$814.63		$881.5462	$881.54	$881.55	$881.70